OA-23 Denial Code: Meaning, Secondary Payer Adjustments, and How to Fix It

A medical practice submits a claim to secondary insurance after the primary payer has processed its portion. The primary payment is recorded, the contractual adjustment has been posted, and the remaining balance is awaiting secondary adjudication.

When the secondary payer’s Electronic Remittance Advice (ERA) arrives, the billing team notices a large adjustment labeled OA-23.

The secondary payment may be smaller than expected, or the remittance may show no additional payment at all.

At first glance, the adjustment can look like another denial, an unexpected contractual write-off, or money the practice has lost.

However, OA-23 does not automatically represent a denied claim or lost reimbursement.

It generally communicates the financial impact of an earlier payer’s adjudication, including payments and adjustments that have already been accounted for.

This distinction is particularly important when a patient has multiple insurance plans. If the billing team misunderstands OA-23 and posts the adjustment as a new write-off, the practice may reduce accounts receivable incorrectly, create artificial credit balances, or misstate the patient’s remaining responsibility.

Similarly, assuming that every OA-23 adjustment requires an appeal can create unnecessary administrative work when the secondary payer has processed the claim correctly.

Understanding the denial code oa 23 begins with recognizing how primary and secondary insurance payments interact and how the remittance communicates amounts that have already been processed.

For medical practices, accurate OA-23 interpretation is essential to reliable payment posting, coordination of benefits, secondary claim reconciliation, and accounts receivable management.

What Is the OA-23 Denial Code in Medical Billing?

OA-23 is a standardized adjustment code combination used on healthcare remittance transactions to identify the impact of prior payer adjudication.

According to X12, Claim Adjustment Reason Code (CARC) 23 describes the impact of previous payer adjudication, including payments and adjustments.

The official definition specifies that CARC 23 must be used with the OA Claim Adjustment Group Code.

The two elements have distinct meanings.

OA: Other Adjustment, the group code used to classify the adjustment.

23: The Claim Adjustment Reason Code describing prior payer adjudication.

Together, OA-23 tells the billing system that the current payer is accounting for financial activity associated with one or more previous payers.

This information is commonly encountered when a secondary or tertiary insurer processes a claim after another insurer has already determined its payment responsibility.

Does OA-23 Mean the Claim Was Denied?

Not necessarily.

Although many billing professionals search for the term “OA-23 denial code,” the adjustment itself does not establish that the secondary payer denied the service.

A secondary claim may contain OA-23 and still receive payment.

Another claim may contain OA-23 with no additional reimbursement because the prior payer’s payment and the secondary payer’s benefits leave no further amount payable.

A third claim may contain OA-23 alongside separate adjustments identifying a genuine coverage or payment dispute.

The billing team must therefore review the complete remittance rather than drawing a conclusion from OA-23 alone.

The key distinction is straightforward:

OA-23 describes the effect of earlier adjudication. It does not independently explain every reason for the current payer’s payment amount.

Why OA-23 Appears on Secondary Insurance Claims

OA-23 is closely connected to coordination of benefits (COB).

Coordination of benefits determines how multiple insurance plans interact when more than one payer potentially covers the same healthcare service.

The primary payer generally processes the claim first.

The secondary payer then considers the primary payer’s adjudication and determines whether an additional payment is due under the applicable plan and COB methodology.

The secondary payer cannot accurately evaluate the claim without understanding the amounts that have already been paid, reduced, or assigned to another party.

This is where OA-23 becomes important.

How Primary Insurance Processes the Claim

Consider a physician who charges $400 for a covered medical service.

The primary insurer determines:

• Original billed charge: $400
• Contractual adjustment: $150
• Allowed amount: $250
• Primary insurance payment: $200
• Patient coinsurance: $50

After the primary payer processes the claim, the provider records the $200 payment and $150 contractual adjustment.

The account now has an outstanding balance of $50.

If the patient has secondary coverage, the practice may submit the claim to the secondary insurer for consideration of the remaining responsibility.

How Secondary Insurance Uses the Primary Payment

The secondary insurer reviews the previous adjudication and applies its own coverage and coordination rules.

It may consider:

• The original charge
• Primary insurance payment
• Primary contractual adjustment
• Remaining patient responsibility
• Applicable secondary benefits
• Coordination methodology
• Secondary payer limitations

The secondary insurer must also communicate which amounts were already accounted for by the primary payer.

OA-23 is used for that prior-payer impact.

It helps the billing system distinguish earlier payments and reductions from financial activity newly created by the secondary payer.

Why OA-23 Is Important for Accurate Payment Posting

Payment posting is one of the most important areas affected by OA-23.

When a practice receives a primary remittance, it typically records the insurer’s payment, applicable contractual adjustments, and the balance assigned to patient responsibility.

Later, when the secondary remittance arrives, the payment-posting team must record only the new financial activity that belongs to that remittance.

The practice should not post the primary insurer’s payment or contractual adjustment again.

Otherwise, the account will no longer accurately represent the amount received and the remaining responsibility.

OA-23 Prevents Duplicate Financial Adjustments

X12’s guidance on secondary payer remittances explains that previous payer payments and contractual reductions should not be repeated as new financial entries.

Instead, the secondary payer uses OA-23 to communicate their effect on the current adjudication.

This provides a standardized way for billing software to distinguish prior activity from current activity.

For example, if the primary insurer already paid $200, that amount should remain recorded as the primary payment.

The secondary insurer’s OA-23 entry does not mean the practice has received another $200.

Similarly, a contractual adjustment previously posted from the primary remittance should not be posted a second time merely because it contributes to the OA-23 amount.

OA-23 should be interpreted as prior-payer impact, not automatically treated as a new payment or write-off.

Understanding OA-23 With a Practical Payment Example

Consider an outpatient medical practice that submits a $400 claim.

The patient has primary and secondary insurance.

Primary Insurance Adjudication

Financial Detail	Amount
Original charge	$400
Primary contractual adjustment	$150
Primary payment	$200
Remaining patient responsibility	$50

The practice posts the $200 primary payment and $150 contractual adjustment.

The remaining account balance is $50.

Secondary Insurance Adjudication

Assume the secondary payer reviews the primary adjudication and determines that it owes an additional $30.

The secondary remittance may communicate the following simplified financial relationship:

Secondary Remittance Detail	Amount
Original charge	$400
OA-23 prior-payer impact	$350
New secondary payment	$30
Final patient responsibility	$20

The $350 OA-23 amount represents the earlier $200 primary payment plus the $150 primary contractual adjustment.

Those amounts have already been posted.

The secondary insurer contributes $30 in new reimbursement.

The remaining $20 represents the patient’s final responsibility in this hypothetical example.

How the Account Should Be Reconciled

The complete account should reflect:

Original charge: $400

Primary payment: $200

Primary contractual adjustment: $150

Secondary payment: $30

Final patient responsibility: $20

The financial activity balances to the original charge.

The $350 OA-23 amount is not another $350 adjustment to be posted.

If the billing system deducted that amount again, it would distort the account and potentially create a false credit balance.

This is one of the most important practical concepts in OA-23 payment posting.

Note: This is an illustrative example. Actual secondary reimbursements and patient responsibility depend on the payer’s COB methodology, benefit design, contract terms, and other applicable requirements.

What Amounts Are Included in OA-23?

OA-23 generally represents amounts arising from prior payer adjudication that have already affected the provider’s accounts receivable.

This may include previous payer payments and applicable contractual or other provider adjustments.

The precise amount depends on the preceding payer’s adjudication and the way the subsequent payer reports the prior-payer impact.

Prior Insurance Payments

If primary insurance paid part of the claim, that payment has already been recorded.

The secondary remittance may include the prior payment as part of the OA-23 calculation.

The amount should not be posted again as new insurance revenue.

Previous Contractual Adjustments

If primary insurance reduced the original charge according to the applicable allowed amount, the contractual adjustment may also contribute to OA-23.

For example:

Original charge: $600

Primary contractual adjustment: $200

Primary insurance payment: $300

Remaining patient responsibility: $100

The previous $200 adjustment and $300 payment may form a $500 prior-payer impact.

That impact does not authorize the billing team to write off another $500.

Other Prior Payer Adjustments

Some claims involve additional adjustment types or multiple earlier payers.

The appropriate OA-23 amount should reflect the previous adjudication according to the applicable X12 reporting requirements.

For tertiary claims, the prior-payer impact may relate to more than one preceding insurer.

The billing team should therefore review the relevant remittance history rather than assuming that OA-23 always represents one primary payment.

OA-23 vs. CO-45: Understanding the Difference

OA-23 and CO-45 can both appear on healthcare remittances, but they communicate different financial concepts.

OA-23: Impact of Prior Adjudication

OA-23 describes earlier payer payments and adjustments affecting the current payer’s adjudication.

It is used with the OA group code.

The amount represents previously reported financial activity and should not be automatically deducted from accounts receivable again.

CO-45: Current Contractual Adjustment

CO-45 generally indicates that a charge exceeds the applicable fee schedule, maximum allowable amount, or contracted or legislated fee arrangement.

It is commonly used to communicate a contractual reduction resulting from the current payer’s adjudication.

The important distinction is that a secondary payer should not report a previous payer’s contractual adjustment again as a new CO-45 adjustment.

If the secondary payer creates an additional legitimate contractual reduction, that current adjustment may be separately reported using the applicable code.

Comparison

Area	OA-23	CO-45
Purpose	Reports prior-payer impact	Reports an allowable or contractual reduction
Adjustment group	OA	CO or PR, as applicable
Related payer activity	Previous adjudication	Current payer’s applicable adjustment
Posting treatment	Avoid reposting prior amounts	Post valid new adjustment according to liability
Main risk	Duplicate payment or adjustment posting	Incorrect contractual write-off or allowed amount

This distinction becomes especially important when billing software imports primary and secondary 835 transactions automatically.

For a detailed explanation of allowable amounts, see PROMBS’s guide to CO-45 in medical billing.

OA-23 vs. CO-22: Why These Codes Are Not Interchangeable

Another important comparison involves CO-22.

CARC 22 indicates that a service may be covered by another payer under coordination-of-benefits rules.

It may appear when the payer believes another insurer has responsibility for the claim.

For example, a claim may be submitted to an insurer that identifies itself as secondary rather than primary.

The payer may require the claim to be processed by the appropriate primary insurer first.

That is a different issue from OA-23.

CO-22 concerns potential responsibility involving another payer.

OA-23 describes the financial impact of adjudication already performed by a previous payer.

Although both may appear in coordination-of-benefits situations, they should not automatically trigger the same follow-up.

If CO-22 appears, the billing team may need to verify payer order or other insurance information.

If OA-23 appears, the team should examine how prior payments and adjustments were included in the secondary adjudication.

PROMBS covers these broader problems in Secondary Claims Denied After Primary Payment: Fixing Coordination-of-Benefits Errors.

Can OA-23 Appear When Secondary Insurance Pays Nothing?

Yes.

A secondary payer may report OA-23 even when it issues no additional reimbursement.

This can happen because the previous payer’s adjudication has already satisfied the amount payable under the secondary plan’s applicable rules.

For example, the primary insurer may have paid an amount equal to or greater than what the secondary plan would otherwise contribute under its coordination methodology.

The secondary payer may therefore determine that no additional payment is due.

The OA-23 adjustment communicates the prior-payer impact, but the absence of a new payment is not automatically evidence of incorrect adjudication.

Does a Zero-Dollar Secondary Payment Mean a Denial?

Not necessarily.

A zero-dollar secondary payment can be a correct outcome under coordination-of-benefits rules.

However, it can also occur when the secondary payer has incomplete information, applies the wrong benefit calculation, or incorrectly interprets prior payer activity.

The billing team should examine the complete remittance before deciding whether additional reimbursement is due.

Important questions include:

• Was the primary payment reported correctly?
• Did the secondary payer receive accurate COB information?
• Was the applicable benefit calculation correct?
• Was the patient responsibility reported accurately?
• Were there any separate denial or adjustment codes?
• Was a secondary payment expected under the plan?

The answer depends on the full claim and benefit information, not OA-23 alone.

Can the OA-23 Amount Be Billed to the Patient?

No amount should be transferred to the patient merely because it appears under OA-23.

The code reports prior-payer adjudication impact rather than identifying new patient responsibility.

Patient responsibility is communicated through the applicable adjudication information, including relevant PR adjustments where appropriate.

Before sending a patient statement, the billing team should reconcile the primary and secondary remittances and confirm the final amount that may legally and contractually be collected.

Why Incorrect Patient Billing Happens

Some billing systems may misinterpret adjustment codes when payment-posting rules are not configured correctly.

If a prior-payer adjustment is treated as a new financial obligation or incorrectly changes the patient balance, the system may generate an inaccurate statement.

This can create patient confusion, unnecessary collections activity, and additional work for the practice.

Accurate OA-23 configuration helps ensure that previous payer amounts are not confused with new patient responsibility.

What Is the Difference Between OA-23 and a Payer Recoupment?

OA-23 should not be confused with a payer recovery transaction.

A recoupment generally involves a payer seeking to recover money that it previously paid.

The recovery may occur through an offset against future payments, a refund request, or another applicable process.

OA-23, by contrast, describes the impact of earlier payer adjudication on the current payer’s handling of the claim.

It does not independently indicate that the secondary insurer has recovered money from the provider.

Why This Distinction Matters

Suppose the primary insurer previously paid $400.

The secondary insurer later reports OA-23 as part of its claim adjudication.

That entry does not mean the secondary insurer has taken back the original $400.

If a payer actually recoups an overpayment, the billing department must review the recovery transaction separately and reconcile it with the original account.

Confusing prior-payer impact with recoupment activity can result in incorrect posting and misleading accounts receivable balances.

Why OA-23 Can Create False Credit Balances

One of the most serious consequences of incorrect OA-23 interpretation is the creation of artificial negative balances.

A credit balance generally appears when posted payments and adjustments exceed the amount recorded as outstanding.

However, not every negative balance represents a genuine overpayment.

For example, a practice may correctly post a $300 primary payment and a $200 primary contractual adjustment.

If its billing software subsequently posts a $500 OA-23 amount as another contractual reduction, the account may show an artificial credit.

No additional $500 was received or legitimately written off by the secondary payer.

The error occurred because the system counted earlier financial activity twice.

Why This Creates Financial Risk

Incorrect adjustment posting can:

• Distort accounts receivable
• Create false patient or payer credits
• Misstate outstanding reimbursement
• Trigger unnecessary refund investigations
• Produce inaccurate financial reports
• Make payment reconciliation more difficult
• Hide genuine underpayments

If a false credit is mistaken for an actual overpayment, the practice may even issue an unnecessary refund.

That is why OA-23 posting errors should be investigated before any account correction or refund decision is finalized.

Why OA-23 Should Not Automatically Trigger a Claim Appeal

An OA-23 entry does not, by itself, establish that the secondary payer made an incorrect payment decision.

Submitting an appeal solely because OA-23 appears on the remittance is therefore not an effective denial-management strategy.

Before considering a dispute, the billing team should determine whether the secondary insurer applied the correct COB information and benefit rules.

When Further Investigation May Be Appropriate

Additional research may be justified when:

• The primary payment reported by the secondary insurer does not match the actual primary EOB.
• The secondary payer used the wrong coordination-of-benefits information.
• The secondary payment appears inconsistent with applicable plan rules.
• Patient responsibility does not reconcile with the remittances.
• A duplicate adjustment created an incorrect account balance.
• The secondary payer did not consider an appropriate corrected primary adjudication.
• A legitimate secondary payment appears to be missing.

The goal is to identify an actual processing or calculation problem.

Only then can the practice determine whether payer clarification, reprocessing, a corrected submission, or a formal dispute is appropriate.

How OA-23 Affects Medical Practice Revenue

Although OA-23 is ordinarily an informational adjustment, mishandling it can create financial and operational consequences.

A practice may believe that insurance reimbursement was reduced when the secondary payer actually processed the claim correctly.

Alternatively, an incorrect posting rule may hide an unpaid balance or create an artificial credit.

Both situations interfere with accurate revenue-cycle reporting.

Accounts Receivable Accuracy

If the billing system duplicates previous payments or adjustments, the recorded balance may no longer represent the actual amount outstanding.

This can make A/R reports unreliable and complicate follow-up prioritization.

Payment Posting Efficiency

When automated ERA posting handles OA-23 incorrectly, billing staff may need to reverse adjustments, rebuild account histories, and manually reconcile multiple remittances.

This increases administrative workload.

Secondary Claim Follow-Up

A misunderstood OA-23 entry may cause staff to pursue unnecessary appeals while genuine secondary underpayments remain unidentified.

The team needs to distinguish a valid zero-dollar payment from a secondary claim that requires further action.

Patient Account Accuracy

Incorrect reconciliation can also change the patient balance, potentially creating unnecessary statements, collection activity, or refund investigations.

Revenue Cycle Reporting

Repeated OA-23 posting errors can affect payment analysis, credit-balance reporting, outstanding A/R, and payer performance reviews.

Organizations should therefore treat accurate secondary remittance interpretation as an essential part of revenue-cycle financial controls.

PROMBS supports healthcare practices with revenue cycle management services that encompass payment posting, insurance follow-up, claim reconciliation, and broader billing administration.

Why Accurate Coordination of Benefits Is Essential

The most effective OA-23 management begins before the secondary remittance arrives.

Practices should identify the correct primary and secondary insurance order and submit accurate prior-payer adjudication information when required.

If a secondary insurer receives incomplete or incorrect primary payment details, the resulting adjudication may not reflect the actual financial history.

Similarly, if the primary claim is later corrected or reprocessed, the billing department may need to determine whether the secondary claim also requires review.

For medical practices, the objective is not merely to submit the claim to multiple insurance companies.

It is to maintain a consistent financial record showing:

Original charge → primary adjustment → primary payment → secondary adjudication → secondary payment → final responsibility.

OA-23 helps communicate part of this financial relationship.

When the adjustment is interpreted correctly, the practice can avoid duplicate posting and better distinguish legitimate secondary payer outcomes from errors requiring investigation.

The Most Important Principle for Understanding OA-23

OA-23 should not be treated as a standard denial requiring immediate appeal, another contractual write-off, or an amount automatically billable to the patient.

Its purpose is to communicate how previous insurance adjudication affects the current payer’s payment calculation and remittance reporting.

Before changing the account balance, the billing team should establish which payments and adjustments were already recorded and which amounts represent new activity from the secondary insurer.

This distinction protects the accuracy of accounts receivable and provides a reliable foundation for resolving genuine payment discrepancies.

An effective denial code OA 23 investigation therefore begins with the complete financial history, not the adjustment label alone.

How to Resolve OA-23 Adjustments in Medical Billing

Resolving an OA-23 adjustment begins with understanding the complete financial history of the claim rather than attempting to remove the adjustment from the secondary payer’s remittance.

Unlike many traditional denial codes, OA-23 generally communicates the impact of adjudication by an earlier insurer. It does not necessarily indicate that the secondary payer rejected the claim, reduced reimbursement incorrectly, or requested additional information.

In many cases, no correction is necessary because the secondary payer has processed the claim appropriately.

However, an OA-23 adjustment requires investigation when the reported amount does not reconcile with previous payer activity, the billing system creates an incorrect account balance, or the secondary insurer appears to have used inaccurate coordination-of-benefits information.

The proper workflow is:

Review primary adjudication → inspect secondary remittance → identify OA-23 → reconcile prior payments and adjustments → verify new secondary activity → confirm patient responsibility → resolve discrepancies.

This process helps billing teams distinguish legitimate secondary payment outcomes from actual errors requiring correction or payer follow-up.

Step 1: Retrieve the Original Primary EOB or ERA

The first step is to obtain the primary insurer’s complete adjudication information.

The primary Explanation of Benefits (EOB) or Electronic Remittance Advice (ERA) establishes what happened when the first payer processed the claim.

The billing team should verify:

• Original billed charges
• Primary payer’s allowed amount
• Primary insurance payment
• Contractual adjustments
• Deductible
• Copayment
• Coinsurance
• Other applicable adjustments
• Claim control number
• Dates of service
• CPT or HCPCS codes
• Service-line payment details

These details provide the foundation for understanding the subsequent OA-23 adjustment.

Why the Primary EOB Matters

Suppose a physician submits a claim for $500.

The primary insurer determines that the allowed amount is $350.

The insurer pays $280 and assigns the remaining $70 to patient coinsurance.

The primary remittance reflects:

Primary Adjudication	Amount
Original charge	$500
Contractual adjustment	$150
Insurance payment	$280
Patient responsibility	$70

The practice should already have recorded the $280 payment and $150 adjustment.

When the secondary remittance arrives, those amounts should not be posted again.

The remaining $70 represents the amount requiring further financial disposition, subject to secondary coverage and applicable patient billing rules.

Step 2: Review the Secondary Payer’s 835 Remittance

After reviewing the primary adjudication, retrieve the secondary payer’s complete remittance.

The 835 Electronic Remittance Advice communicates the secondary insurer’s adjudication and financial determination.

It may include:

• Original billed amount
• Secondary payment
• OA-23 adjustment
• Additional contractual adjustments
• Remaining patient responsibility
• Other claim adjustment codes
• Remittance advice remark codes
• Claim processing status

The billing team should determine how these elements relate to the original primary payer activity.

What to Look for in the Secondary ERA

The most important question is whether the remittance separates previously reported financial activity from new secondary payer activity.

Previous financial activity may include payments and contractual reductions already posted after primary adjudication.

New activity may include the secondary insurer’s payment, a legitimate additional adjustment, or its determination of remaining patient responsibility.

The two categories should not be mixed.

For example, an OA-23 amount of $350 does not automatically mean the secondary insurer denied $350 of reimbursement.

It may represent the previous payer’s $200 payment and $150 contractual adjustment that have already affected the account.

The secondary payment must be evaluated separately.

Step 3: Identify Where OA-23 Appears in the 835

OA-23 is generally reported using the Claim Adjustment Group Code OA and Claim Adjustment Reason Code 23.

In the electronic 835 transaction, claim adjustments are communicated through CAS segments.

The adjustment can appear at an applicable claim or service-line level, depending on how the remittance reports the adjudication.

A simplified representation might appear as:

CAS*OA*23*350~

This indicates an OA-23 adjustment amount of $350.

However, the billing team should not interpret this segment in isolation.

The complete remittance is needed to understand how the original charge, previous payer activity, current payer payment, and remaining adjustments balance.

Why Claim-Level and Service-Line Details Matter

Some claims contain several billable services.

The payer may report prior adjudication impact at the service-line level rather than presenting a single amount for the entire claim.

If a billing system incorrectly maps service-level adjustments into claim-level posting entries, account reconciliation may become inaccurate.

The practice should therefore verify that the payment-posting system interprets the remittance at the level where the payer reported the information.

Step 4: Reconcile Prior Payer Payments and Adjustments

The next step is to compare the OA-23 amount with the primary payer’s previously reported financial activity.

X12 explains that OA-23 helps communicate prior adjudication without causing the provider to post the same payment or contractual reduction more than once.

In a straightforward example, the OA-23 amount may correspond to the total of the previous payer’s payment and contractual adjustment.

However, it is important to understand that OA-23 is not universally calculated by simply adding every field on the primary EOB.

The amount depends on the reporting rules and how the subsequent payer’s adjudication accounts for earlier financial activity.

For example, some situations require separate treatment of prior patient responsibility or other adjustment groups. An OA-23 amount may also differ from a simple payment-plus-adjustment calculation when the subsequent payer’s adjudication changes the impact of earlier adjustments.

The billing team should therefore use the complete primary and secondary remittances rather than rely on one fixed formula.

Questions to Ask During Reconciliation

• Does OA-23 represent previously processed financial activity?
• Have those amounts already been posted?
• Is the primary payment accurate?
• Are the primary contractual adjustments recorded correctly?
• Did the secondary payer use the correct previous adjudication information?
• Are there additional adjustments created by the secondary payer?
• Does the complete secondary remittance balance to the original charge?

These questions help determine whether the OA-23 entry is correct.

Step 5: Verify the Secondary Payment Calculation

After confirming the prior payer information, review the amount the secondary insurer actually paid.

A secondary payer does not necessarily pay the entire balance left by primary insurance.

Its reimbursement depends on its own benefits and coordination-of-benefits methodology.

For example, a primary insurer may assign $100 to patient coinsurance, but the secondary insurer may pay only $60.

That does not automatically mean $40 was incorrectly denied.

The secondary plan may have different allowed amounts, benefit limitations, or coordination provisions.

What Should Be Verified?

Review the secondary plan’s applicable coverage and payment rules.

Then compare those rules with:

• Original billed charge
• Primary payment
• Primary adjustments
• Applicable secondary allowed amount
• Secondary payment
• Additional current-payer adjustments
• Final patient responsibility

The goal is to determine whether the secondary insurer’s calculation is consistent with the applicable plan.

Step 6: Confirm Final Patient Responsibility

One of the most important parts of OA-23 reconciliation is identifying the amount, if any, that remains collectible from the patient.

The original primary EOB may assign a deductible, copayment, or coinsurance amount to the patient.

However, secondary adjudication can reduce or otherwise affect that responsibility.

The billing department should not automatically transfer the primary payer’s remaining amount to the patient before reviewing secondary insurance.

Why Final Responsibility Can Change

For example, primary insurance may assign $80 in coinsurance.

Secondary insurance may pay $50.

If the applicable benefit and contractual rules leave the remaining $30 as patient responsibility, that becomes the relevant amount for the final account.

However, patient liability can be affected by provider contracts, program requirements, and applicable billing protections.

For some patients, such as certain Medicare beneficiaries protected by Qualified Medicare Beneficiary rules, additional restrictions may apply.

Therefore, the final statement should reflect verified patient responsibility, not simply the difference between the original charge and total insurance payments.

Step 7: Review Duplicate Payment and Adjustment Posting

A common OA-23 problem occurs when the practice-management system posts previously recorded amounts again.

This often happens when automated ERA posting rules do not correctly distinguish prior-payer impact from new secondary activity.

Common Posting Errors

These may include:

• Posting OA-23 as another contractual adjustment
• Reposting the primary insurance payment
• Posting the primary contractual adjustment twice
• Treating OA-23 as new patient responsibility
• Applying the adjustment to the wrong service line
• Incorrectly mapping secondary CAS segments
• Reprocessing the same ERA more than once

The account may appear fully resolved even though money remains collectible.

Alternatively, duplicate posting can produce a false credit balance.

Both outcomes can distort financial reporting.

Practical Example 1: Correct OA-23 Reconciliation

Consider a medical practice that bills $400 for an office visit.

The patient has primary and secondary insurance.

Primary Payer Adjudication

The primary insurer processes the claim as follows:

Description	Amount
Original charge	$400
Primary contractual adjustment	$150
Primary payment	$200
Remaining patient coinsurance	$50

After primary payment posting, the account shows $50 outstanding.

Secondary Payer Adjudication

Assume the secondary insurer reviews the primary adjudication and determines that it owes another $30.

Its remittance reports the following simplified relationship:

Description	Amount
Original charge	$400
OA-23 prior-payer impact	$350
New secondary payment	$30
Final patient responsibility	$20

The $350 OA-23 amount represents the prior $200 payment and $150 contractual reduction in this example.

The secondary insurer pays $30.

The remaining $20 is assigned to the patient under the assumed benefit rules.

Correct Payment Posting

The practice should record:

• Original charge: $400
• Primary contractual adjustment: $150
• Primary insurance payment: $200
• Secondary insurance payment: $30
• Remaining patient balance: $20

The calculation is:

$400 − $150 − $200 − $30 = $20

The account is properly reconciled.

What Should Not Happen

The billing team should not post the $350 OA-23 amount as another adjustment.

Doing so would duplicate financial activity already recorded after primary adjudication.

This example illustrates why OA-23 is normally treated as information about prior payer activity rather than a new write-off.

The amounts are hypothetical and assume no additional secondary contractual adjustment. Actual secondary adjudication depends on the applicable plan and COB rules.

Practical Example 2: OA-23 Creates a False Credit Balance

Now consider a claim where the payment-posting system is incorrectly configured.

Original Claim

The practice submits a $600 claim.

Primary insurance adjudicates:

Description	Amount
Original charge	$600
Primary contractual adjustment	$240
Primary insurance payment	$300
Remaining balance	$60

The practice correctly posts the $240 adjustment and $300 payment.

The account now has $60 outstanding.

Secondary Insurance Processes the Claim

The secondary payer determines that it will pay $40.

Its simplified remittance shows:

Description	Amount
Original charge	$600
OA-23 prior-payer impact	$540
New secondary payment	$40
Remaining patient responsibility	$20

The correct account balance after the secondary payment is:

$600 − $240 − $300 − $40 = $20

The Posting Error

Assume the practice’s automated payment-posting system interprets the $540 OA-23 amount as a new contractual adjustment.

It has already posted the primary payment and adjustment.

Nevertheless, it subtracts another $540 from the account.

The ledger now reflects:

Description	Amount
Original charge	$600
Primary contractual adjustment	−$240
Primary insurance payment	−$300
Secondary payment	−$40
Incorrect additional OA-23 adjustment	−$540
Incorrect account balance	−$520

The billing system now displays a $520 credit.

However, the practice has not received an additional $520.

The negative balance exists because an informational prior-payer adjustment was incorrectly posted as a new financial reduction.

Correct Audit Finding

The account contains a false credit balance created by duplicate adjustment posting.

Correct Resolution

The billing team should verify the source transaction, reverse the incorrect $540 adjustment, confirm the correct primary and secondary activity, and restore the accurate $20 remaining balance.

Incorrect Resolution

Issuing a refund based on the negative balance would be inappropriate because the apparent credit does not establish a true overpayment.

This example demonstrates how an OA-23 posting error can turn a correctly adjudicated secondary claim into a financial reporting problem.

Step 8: Investigate Incorrect Coordination-of-Benefits Information

Sometimes the OA-23 amount is incorrect because the secondary payer received inaccurate information about the primary adjudication.

The problem may originate during the secondary claim submission process.

For example:

The primary insurer pays $250.

However, the secondary claim incorrectly reports that the primary insurer paid $350.

If the secondary payer relies on that information, it may calculate its payment using an inaccurate understanding of what was already paid.

The billing team should compare the information submitted to the secondary payer against the actual primary EOB or ERA.

Common COB Data Problems

• Incorrect primary payer payment amount
• Missing primary contractual adjustment
• Wrong payer order
• Incorrect primary payer identifier
• Incomplete service-line adjudication
• Claim submitted before primary processing was complete
• Outdated primary EOB information
• Corrected primary claim not reflected in secondary records

If the original secondary submission is inaccurate, determine the correction procedure accepted by the payer.

Do not assume the secondary insurer will automatically recalculate its payment without receiving updated information.

Step 9: Compare the Secondary 837 Claim With the Primary Adjudication

Electronic secondary claims can include information about previous payer adjudication.

The 837 healthcare claim transaction communicates the original claim details and applicable other-payer information to the secondary insurer.

The data should correspond to the primary payer’s actual determination.

For example, an electronic professional secondary claim may include relevant information identifying the other payer, earlier payments, and adjudication details at the applicable claim or service-line level.

The billing team should determine whether the transmitted information matches the primary remittance.

Why the Submitted Claim Must Be Reviewed

The practice-management system may show the correct primary payment, while the transmitted 837 includes an inaccurate amount because of an interface or mapping problem.

In that situation, changing the patient’s ledger may not correct the actual issue.

The original electronic submission should be examined to identify what the secondary insurer received.

When Service-Line Detail Matters

A claim may include multiple CPT or HCPCS lines.

The primary payer might:

• Pay one service in full
• Apply coinsurance to another
• Deny a separate service
• Reduce an additional charge contractually

Those adjudications may need to be represented accurately in the secondary submission.

A correct overall payment total does not necessarily prove that the individual service lines were reported correctly.

Step 10: Determine Whether the Secondary Payer Used the Correct COB Methodology

Even if the submitted claim is accurate, the secondary insurer may calculate reimbursement incorrectly.

The billing team should distinguish between an actual payer error and a payment that is lower than expected but consistent with the plan’s benefits.

Depending on the insurance arrangement, the secondary plan may apply different coordination methodologies.

The plan may consider what it would have paid as primary, the amount already paid by the first insurer, its own allowed amount, or other applicable rules.

What to Review Before Disputing the Payment

Confirm:

• Applicable secondary benefit provisions
• Correct primary payment amount
• Accurate prior adjustments
• Secondary allowable amount, where relevant
• Correct patient responsibility
• Any applicable payment limitations
• Relevant payer processing notes

The practice should not assume that the secondary insurer is obligated to pay the entire balance left after primary adjudication.

If the calculation is correct, the account should be reconciled accordingly.

If the calculation appears inconsistent with the plan, additional payer research may be justified.

Step 11: Review Zero-Dollar Secondary Payments

An OA-23 adjustment can appear when the secondary insurer pays nothing.

This is not automatically an error.

For example, a secondary plan may determine that the primary insurer already paid as much as the secondary plan would otherwise owe under its COB methodology.

In that case, no additional secondary payment may be due.

How to Investigate a Zero-Dollar Payment

Start with the primary EOB or ERA.

Then review the secondary remittance and determine whether the payer:

• Correctly recognized the primary payment
• Applied the appropriate benefit rules
• Calculated the prior-payer impact accurately
• Reported any additional adjustments
• Identified final patient responsibility correctly

If those elements are consistent, the $0 payment may be a valid result.

The practice should not categorize the claim as denied solely because the remittance shows OA-23 and no payment.

For broader secondary adjudication problems, see PROMBS’s guide to secondary claim denials after primary payment.

Step 12: Reconcile Corrected Primary Claims and Reprocessing

Primary insurance adjudication does not always remain unchanged.

A claim may later be:

• Corrected
• Reversed
• Reprocessed
• Reconsidered
• Adjusted after an appeal
• Recalculated after eligibility updates

These events can change the amount that should be reflected in the secondary claim.

Example: Primary Payment Changes After Reprocessing

Suppose the primary insurer originally pays $500.

The secondary insurer processes the claim using that payment information.

Later, the primary insurer reprocesses the claim and determines that its correct payment should be $450.

This change may affect the secondary insurer’s previous calculation.

However, it does not automatically mean the secondary insurer owes the $50 difference.

The billing team must review the corrected primary adjudication and determine whether the secondary claim should be reconsidered under the applicable COB rules.

Recommended Review

Verify the original primary payment, subsequent reversal or adjustment, corrected payment, and corresponding secondary adjudication.

Then determine whether additional claim information must be submitted.

The goal is to ensure the secondary payer’s calculation reflects the relevant final primary determination.

Step 13: Check Whether the Account Was Already Corrected

Before making another adjustment, determine whether someone has already worked the account.

A second employee may have previously corrected a posting error, transferred a payment, or submitted a payer reconsideration.

Without reviewing that history, staff may duplicate the correction.

Check:

• Adjustment history
• Payment history
• Refund register
• Claim notes
• ERA posting records
• Previous payer calls
• Reprocessing requests
• Account transfers

A complete audit trail helps establish what actually remains unresolved.

Step 14: Determine Whether Payer Follow-Up Is Necessary

Not every OA-23 adjustment requires payer communication.

When the remittance is correct and the account reconciles, no additional dispute may be needed.

Payer follow-up becomes more relevant when the practice identifies a specific discrepancy.

Examples include:

• Incorrect primary payment recognized by the secondary payer
• Wrong COB information
• Misapplied secondary benefit calculation
• Incorrect claim-level or service-line information
• Missing recognition of corrected primary adjudication
• Secondary remittance inconsistent with documented payer rules

The billing team should identify the exact problem before contacting the payer.

What Should a Payer Inquiry Include?

A clear inquiry may identify:

• Patient and claim reference
• Date of service
• Primary payer
• Primary payment
• Relevant contractual adjustments
• Secondary adjudication
• OA-23 amount
• Specific calculation discrepancy
• Supporting remittance information

The goal is to make the requested correction clear rather than simply asking the payer to reconsider the entire claim.

Step 15: Determine the Correct Resolution

After completing the reconciliation, the account should be classified according to the actual finding.

Audit Finding	Appropriate Resolution
OA-23 correctly reports prior-payer impact	Post only applicable new activity; no OA-23 correction
Primary payment posted twice	Correct duplicate posting
Primary contractual adjustment duplicated	Reverse the incorrect adjustment
Secondary payer used wrong primary payment	Request review or submit corrected COB data as permitted
Secondary payer correctly pays $0	Reconcile the account and verify final responsibility
Secondary payment is inconsistent with applicable benefits	Investigate calculation and consider payer review
Corrected primary claim changed prior adjudication	Determine whether secondary reprocessing is required
Secondary payment posted to wrong encounter	Transfer or correct payment posting
OA-23 created a false credit balance	Remove the improper adjustment and reconcile the ledger
Final patient responsibility is unclear	Review both remittances and applicable billing protections

This approach helps the billing department distinguish financial posting errors from genuine payer disputes.

Step 16: Document the Complete OA-23 Investigation

Every investigated account should contain enough information for another reviewer to understand the findings.

Useful documentation includes:

• Original billed amount
• Primary insurance payment
• Primary adjustments
• Secondary insurance payment
• OA-23 adjustment
• Any additional secondary adjustments
• Final patient responsibility
• Identified discrepancy
• Supporting documents reviewed
• Corrective action taken
• Payer communication
• Final account balance

The documentation should explain whether the adjustment was correctly reported or required correction.

This is especially useful when the practice later encounters another remittance, refund inquiry, payer recovery, or account audit.

Common OA-23 Reconciliation Mistakes

Several recurring mistakes can create avoidable financial problems.

Treating OA-23 as a New Contractual Write-Off

This may duplicate prior payer adjustments and distort accounts receivable.

Assuming OA-23 Means a Denied Claim

The code may appear in a correctly processed secondary claim.

Posting Primary Insurance Payments Twice

A payment already recorded from the primary remittance should not be posted again because it appears in the secondary adjudication history.

Ignoring Corrected Primary Claims

If primary adjudication changes, the secondary payer’s earlier calculation may need to be reviewed.

Transferring the Entire Primary Balance to the Patient

Secondary insurance may cover part of the remaining responsibility.

Automatically Appealing Zero-Dollar Secondary Claims

A $0 secondary payment can be correct under the applicable COB methodology.

Using OA-23 as a Refund Trigger

An OA-23 entry does not establish that the practice received an overpayment.

Failing to Verify Electronic Posting Rules

Automated payment-posting systems can repeatedly create incorrect adjustments when their mapping rules are not configured appropriately.

Build a Standard OA-23 Reconciliation Checklist

Before closing an OA-23 account, confirm:

1. The primary EOB or ERA was reviewed.
2. The primary payment and adjustments are correct.
3. The complete secondary remittance was reviewed.
4. OA-23 was identified at the appropriate reporting level.
5. Prior payments and adjustments were not posted twice.
6. Any new secondary payment was recorded accurately.
7. Additional current-payer adjustments were reviewed.
8. Final patient responsibility was verified.
9. Corrected primary adjudication was considered, when relevant.
10. The account balance reconciles.
11. Any payer dispute is supported by a specific discrepancy.
12. The final resolution is documented.

This checklist can be incorporated into payment-posting procedures, secondary A/R work queues, and periodic internal billing audits.

Why Accurate OA-23 Reconciliation Protects Revenue

OA-23 reconciliation is not simply a technical task involving remittance codes.

It directly affects the quality of the practice’s financial records.

Incorrect posting can create false credits, conceal legitimate outstanding balances, or cause unnecessary patient billing.

Misinterpreting a correctly calculated secondary payment can also lead to repeated appeals that consume staff resources without producing additional reimbursement.

Conversely, failing to investigate an actual COB calculation error may allow legitimate insurance revenue to remain unpaid.

The strongest payment-posting process therefore distinguishes between:

Previous payer activity

New secondary payer activity

Final patient responsibility

Actual financial discrepancies requiring correction

For medical practices, this creates a more reliable foundation for secondary claim management and accounts receivable reconciliation.

PROMBS supports healthcare providers through revenue cycle management services that include medical billing, payment posting, insurance follow-up, and financial reconciliation.

The goal is not to eliminate OA-23 from remittances. It is to ensure the adjustment is interpreted correctly and that the account accurately reflects what each payer paid, adjusted, or left outstanding.

Understanding OA-23 is important, but preventing the financial errors associated with its interpretation is equally valuable for medical practices.

A secondary insurance remittance may correctly report the impact of prior payer adjudication. However, if the practice-management system interprets that information incorrectly, the account may develop an artificial credit balance, an inaccurate contractual adjustment, or an outstanding amount that does not reflect actual payer responsibility.

These problems often arise when payment-posting rules are not designed to distinguish previously recorded financial activity from new transactions generated by the secondary insurer.

An effective prevention strategy should connect coordination-of-benefits verification, primary and secondary claim reconciliation, ERA automation, payment-posting validation, and accounts receivable monitoring.

The objective is not to prevent OA-23 from appearing on a remittance. OA-23 is a legitimate adjustment code used to communicate prior payer activity.

The objective is to ensure that the information represented by OA-23 does not create duplicate payments, duplicate adjustments, incorrect patient balances, or missed reimbursement opportunities.

Why OA-23 Should Be Managed as a Reconciliation Issue

One of the most common misconceptions is that every remittance adjustment represents a financial loss requiring denial management.

OA-23 works differently.

The adjustment describes the impact of earlier payer adjudication. The corresponding amounts may already have reduced the practice’s accounts receivable through primary insurance payments or contractual adjustments.

Consequently, an OA-23 investigation should begin with the financial history of the claim.

The billing team needs to establish whether the secondary payer used accurate prior-payer information, whether the secondary payment was calculated correctly, and whether the resulting transactions were recorded appropriately.

If those elements reconcile, no corrective action may be necessary.

However, when a discrepancy exists, the team should determine whether it originated with the insurer, the secondary claim submission, or the practice’s internal posting process.

This distinction prevents staff from submitting unnecessary appeals when the real problem is an accounting error.

1. Validate Coordination of Benefits Before Secondary Claim Submission

Accurate coordination-of-benefits information is essential to avoiding payment discrepancies.

When a patient has multiple insurance plans, the billing department must establish the correct payer order for the applicable date of service.

The primary insurer generally processes the claim first. The secondary insurer then considers the relevant previous adjudication under its own coverage and coordination rules.

Problems can develop when the practice uses outdated insurance information, submits to the wrong payer, or transmits incomplete primary adjudication details.

Common COB Verification Problems

A patient may change employers, obtain coverage through a spouse, become eligible for Medicare, or experience another change affecting payer responsibility.

If the practice continues using an outdated insurance sequence, the secondary insurer may process the claim using incorrect information.

For example, the secondary payer may believe it is primary, while the practice’s records identify another insurer as responsible for the first payment.

That discrepancy must be resolved before the financial calculation can be evaluated reliably.

Recommended Prevention Controls

Practices should verify the relevant coverage information during registration and update payer records when patients report insurance changes.

For secondary claims, staff should confirm that the primary adjudication is complete and that the information transmitted to the secondary payer corresponds to the actual EOB or ERA.

This reduces the likelihood of inaccurate prior-payment reporting and unnecessary secondary claim corrections.

For a broader explanation, see PROMBS’s guide to secondary claim denials after primary payment.

2. Configure ERA Posting Rules to Recognize OA-23 Correctly

Automated payment posting can improve efficiency, but incorrect configuration can multiply financial errors across a large number of claims.

An 835 remittance may contain several adjustment categories.

Some represent amounts the practice should post as current financial transactions. Others communicate financial activity that has already been recorded.

OA-23 belongs to the second category.

The official X12 guidance explains that prior-payer payments and contractual reductions should not be posted again simply because they appear in a subsequent payer’s remittance.

What an Accurate Posting System Should Do

An appropriately configured system should recognize the OA-23 adjustment and use it to reconcile earlier payer activity without creating another independent contractual write-off.

It should separately identify:

• New secondary payer payments
• Legitimate new adjustments
• Remaining patient responsibility
• Previously recorded primary payer activity

For example, if a primary insurer already paid $300 and the practice posted that amount, an OA-23 entry reflecting the prior adjudication should not generate another $300 payment entry.

Similarly, a primary contractual reduction should not be repeated as a new write-off.

Why Automated Posting Rules Need Testing

A software configuration may work correctly for simple claims but fail when a remittance contains multiple service lines, corrected primary payments, or additional secondary adjustments.

Practices should therefore test the posting logic against different adjudication scenarios.

These may include secondary payments greater than zero, legitimate zero-dollar payments, multi-line claims, corrected primary adjudication, and remittances containing new contractual adjustments in addition to OA-23.

Testing should confirm that the final account balance reflects the complete adjudication without counting any transaction twice.

3. Reconcile Primary and Secondary Payments at the Service-Line Level

Claim-level totals can sometimes conceal errors involving individual procedures.

Consider a claim containing three services.

The primary insurer may pay one service, apply coinsurance to another, and deny the third.

When the secondary insurer processes the claim, the previous adjudication may need to be communicated at the appropriate service-line level.

If the billing system records only an overall primary payment without preserving the necessary detail, the secondary payer may receive an incomplete picture of the original adjudication.

This can create inaccurate secondary payment calculations or reconciliation difficulties.

What the Billing Team Should Compare

For affected claims, compare the service-line charges, CPT or HCPCS codes, units, primary payments, primary adjustments, secondary payments, and remaining responsibility.

The goal is to determine whether each line reflects the actual payer decisions.

The practice should also examine whether the OA-23 amount was reported at the claim level or service-line level and whether the billing system interpreted it correctly.

A correctly balanced claim total does not always establish that the individual service lines were posted accurately.

4. Distinguish Legitimate Secondary Underpayments From Correct COB Outcomes

A secondary insurer is not automatically required to pay the entire amount left after primary insurance.

Its responsibility depends on the applicable benefits and coordination-of-benefits methodology.

Consequently, a secondary payment that is smaller than the remaining primary balance is not necessarily an underpayment.

The billing department should establish what the secondary insurer was obligated to pay before categorizing the difference as recoverable revenue.

Example: Correct Secondary Payment

Suppose primary insurance assigns $90 to patient coinsurance.

The secondary insurer reviews the claim and pays $60.

If the secondary plan’s applicable provisions support that $60 payment and the remaining $30 is properly assigned, the claim may have been processed correctly.

The practice should not automatically dispute the remaining $30 merely because the secondary insurer paid less than the original coinsurance amount.

Example: Potential Secondary Underpayment

Now assume the secondary payer calculates its reimbursement using an incorrect primary payment of $350 when the actual primary payment was $250.

If that discrepancy affects the secondary reimbursement calculation, additional payer review may be appropriate.

The billing team should provide the correct primary adjudication information and identify the specific calculation problem.

The objective is to recover reimbursement that is legitimately owed, not to challenge every smaller-than-expected payment.

5. Understand OA-23 and Medicare Secondary Payer Rules

Medicare introduces additional coordination requirements because the program may act as either the primary or secondary payer, depending on the beneficiary’s circumstances.

The Medicare Secondary Payer (MSP) provisions establish situations in which another insurer or entity has primary payment responsibility and Medicare pays second.

Examples may involve certain employer group health plans, workers’ compensation, or other coverage arrangements, subject to the applicable statutory and regulatory rules.

When Medicare Is the Secondary Payer

If Medicare is secondary, the billing department generally must determine whether another payer has primary responsibility and provide appropriate information about that payer’s adjudication.

The previous insurer’s payment and adjustment information can affect Medicare’s secondary payment calculation.

The resulting Medicare remittance may communicate prior-payer impact through OA-23.

However, the presence of OA-23 does not independently determine whether Medicare’s secondary calculation is correct.

The billing team must evaluate the complete claim information and relevant MSP requirements.

Why Medicare Secondary Claims Require Careful Review

Medicare secondary payment calculations may involve rules that differ from ordinary commercial coordination-of-benefits arrangements.

For example, Medicare’s payment may depend on the primary payer’s responsibility and the applicable Medicare payment methodology.

The practice should not assume Medicare automatically pays all remaining charges after the primary insurer processes the claim.

Billing staff should review relevant CMS instructions, primary payment records, and the final Medicare remittance.

The CMS Medicare Secondary Payer overview provides the foundational program requirements.

Medicare as Primary Insurance

When Medicare processes a claim first and another insurer provides supplemental or secondary coverage, the subsequent insurer may use the Medicare adjudication information when calculating its own payment.

This creates another situation where OA-23 can appear on the secondary remittance.

The practice must reconcile the original Medicare payment and adjustments before posting the supplemental insurer’s new financial activity.

6. Apply Patient Billing Protections Before Issuing Statements

Correct payment posting does not automatically establish that an outstanding balance can be billed to the patient.

Patient responsibility depends on the final adjudication, provider agreements, applicable benefit rules, and relevant legal protections.

This is especially important when Medicare and Medicaid are involved.

Qualified Medicare Beneficiary Protections

The Qualified Medicare Beneficiary (QMB) program provides important billing protections for eligible Medicare beneficiaries.

Federal law generally prohibits providers and suppliers from billing QMB beneficiaries for Medicare Part A and Part B cost-sharing associated with Medicare-covered services.

This applies even when a Medicaid program pays less than the full Medicare cost-sharing amount or makes no additional payment.

Accordingly, a secondary remittance showing no additional payment does not automatically authorize the practice to collect the remaining Medicare cost-sharing from a QMB patient.

Practices should verify the beneficiary’s applicable status and review the relevant program rules before generating a patient statement.

For more information, consult the CMS Qualified Medicare Beneficiary Program.

Why This Matters for OA-23

OA-23 reports prior-payer financial activity.

It does not independently establish patient liability.

The billing system should therefore avoid treating the OA-23 amount as collectible patient responsibility.

Final patient balances must be based on the complete adjudication and applicable billing requirements.

7. Prevent False Credit Balances and Unnecessary Refunds

Incorrect OA-23 posting can create artificial negative balances.

These balances may appear to represent excess insurance reimbursement even though the practice did not receive additional money.

For example, a primary payment and contractual reduction may already be recorded correctly.

If the system later deducts the OA-23 amount again, the account may show a credit balance that exists only because of duplicate adjustment posting.

A refund based on that artificial credit could create a financial loss.

How to Investigate a Credit Created After Secondary Posting

The billing team should compare the account balance immediately before and after the secondary ERA was posted.

Next, verify which transactions were newly created.

If the secondary remittance caused previously recorded payments or adjustments to be duplicated, the practice should correct those entries and recalculate the account balance.

Before approving any refund, confirm that an actual overpayment was received and that the funds have not already been returned or recovered.

The same principle applies to payer recoupments.

If an insurer has already recovered an overpayment through an offset, the practice should not issue another refund without verifying the original recovery.

PROMBS discusses related risks in its article on payer recoupment disputes.

8. Establish a Dedicated Secondary Payment Reconciliation Workflow

Secondary insurance claims should not be managed solely through the same workflow used for ordinary primary claim posting.

The financial history is more complex because multiple insurers may have contributed payments or adjustments.

A structured workflow should begin with the primary adjudication and continue through the final secondary determination.

Each account should contain enough information to establish:

• The original billed charge
• Primary payer payment and adjustments
• Secondary payer payment
• Prior-payer impact reported through OA-23
• Any additional current-payer adjustments
• Final patient responsibility
• Outstanding insurance balance, if any
• Required correction or follow-up

The billing team should classify any unresolved discrepancy before transferring the account into a denial, refund, patient collection, or payer follow-up queue.

Why Centralized Reconciliation Matters

When different employees manage primary payments, secondary payments, and refunds independently, financial errors may go unnoticed.

One employee may post the primary adjustment correctly.

Another may later interpret OA-23 as an additional write-off.

A third may approve a refund based on the resulting negative balance.

Centralized account history and clear posting rules help prevent these disconnected decisions.

9. Build Exception-Based OA-23 Monitoring

Not every OA-23 entry requires manual investigation.

In a properly functioning payment-posting system, many secondary remittances can be reconciled accurately without extensive research.

The stronger approach is to identify exceptions that suggest an actual problem.

High-Priority OA-23 Exceptions

Examples include:

Negative balances after secondary ERA posting: May indicate duplicate adjustments or payments.

Unexpected patient responsibility: May reflect incorrect posting or incomplete COB reconciliation.

OA-23 amount inconsistent with available prior adjudication: Requires review of the full remittances and reporting methodology.

Zero-dollar secondary payments with an unexplained calculation: May justify verification of the secondary plan’s benefits.

Multiple secondary remittances for the same claim: May involve reprocessing, reversals, or duplicate transactions.

Corrected primary claims without updated secondary reconciliation: May require review of the secondary adjudication.

These exceptions allow billing teams to concentrate on accounts where financial accuracy is genuinely at risk.

10. Track the Right OA-23 and Secondary Billing KPIs

Payment-posting performance should be measured through financial accuracy and resolution quality, not simply the number of adjustments processed.

A practice may encounter many legitimate OA-23 entries because it serves patients with multiple insurance plans.

That does not mean the practice has a high denial rate.

The more useful question is whether the secondary claims are being reconciled correctly.

KPI	What It Measures
Secondary payment posting accuracy	Percentage of audited secondary remittances posted correctly
OA-23 posting error rate	Percentage of OA-23 remittances with confirmed posting errors
Secondary reconciliation turnaround	Time from receipt of secondary remittance to accurate account reconciliation
False credit balance rate	Frequency of artificial credit balances caused by posting or adjustment errors
COB discrepancy rate	Percentage of reviewed secondary claims with confirmed inaccurate prior-payer data
Secondary payment variance	Difference between expected reimbursement under verified terms and actual secondary payment
Corrected secondary claim rate	Share of secondary claims requiring correction due to submission inaccuracies
Actual additional collections	Verified payments received after successful secondary payer follow-up

Why Reporting Definitions Matter

The practice should define each metric consistently.

For example, the OA-23 posting error rate should count confirmed posting errors rather than every remittance containing OA-23.

Similarly, secondary payment variance should be calculated from verified contract and benefit expectations, not simply from the difference between charges and payments.

A high-dollar charge does not necessarily represent an equivalent reimbursement opportunity.

Accurate definitions help leadership distinguish real revenue problems from ordinary coordination-of-benefits activity.

11. Conduct Monthly OA-23 Payment Posting Audits

A recurring payment-posting audit helps determine whether secondary remittances are being processed correctly.

The review should include both accounts with apparent problems and a sample of accounts that appear fully reconciled.

This is important because some posting errors may incorrectly close the account without generating an obvious denial or outstanding balance.

Review High-Risk Accounts

Prioritize negative balances, unexplained adjustments, unusual patient responsibility, repeated secondary remittances, corrected primary claims, and discrepancies between payer records and internal ledgers.

Compare Actual Remittance Activity

For each sampled account, review the primary ERA or EOB, secondary ERA, OA-23 information, posted payments, adjustments, and final balance.

Confirm that the account reflects the actual financial transactions.

Identify Recurring Patterns

If several accounts contain the same error, determine whether the problem originates from a particular payer, posting configuration, service type, or electronic transaction mapping.

For example, a software rule may incorrectly post claim-level OA-23 entries while handling service-line entries correctly.

The appropriate response would involve reviewing the system configuration and testing affected transactions.

Document Corrective Actions

The audit should identify the error, affected accounts, correction performed, reviewer, and any necessary software or workflow changes.

Follow-up testing should confirm that the same issue no longer affects new remittances.

12. Root-Cause Analysis: Fix the Process, Not Just the Account

An effective OA-23 review should produce operational improvements.

If the practice repeatedly corrects individual accounts without addressing the source of duplicate posting, the same errors may continue.

For example, a recurring false credit balance may originate from a payment-posting rule that interprets every CAS adjustment as a new contractual reduction.

Manual account corrections will not prevent future errors until that rule is changed.

Similarly, repeated secondary payment discrepancies may result from an incorrect primary-payment field in the electronic claim interface.

The long-term solution is to correct the data transfer process, not simply contact the secondary insurer for every affected claim.

A mature revenue-cycle operation uses reconciliation findings to improve its systems, staff workflows, and payer-specific knowledge.

How PROMBS Helps Practices Manage OA-23 and Secondary Insurance Reconciliation

Medical practices should be able to understand their outstanding balances without repeatedly reconstructing complicated insurance payment histories.

However, secondary insurance claims can become difficult to manage when payer adjudications, contractual adjustments, electronic remittances, and patient responsibility are not properly aligned.

Pro Medical Billing Solutions (PROMBS) supports healthcare providers with medical billing, payment posting, denial management, accounts receivable follow-up, and revenue cycle management.

Our services help practices investigate payment discrepancies, improve financial accuracy, and strengthen insurance reimbursement workflows.

Accurate Primary and Secondary Payment Posting

PROMBS supports the accurate recording of insurance payments and adjustments across multiple payer transactions.

By reviewing the relationship between primary and secondary remittances, practices can reduce unnecessary duplicate posting and improve account reconciliation.

Coordination-of-Benefits Review

Our billing teams help practices investigate secondary claim problems involving payer responsibility, incomplete prior-payer information, and discrepancies between the submitted claim and actual adjudication.

Accurate coordination helps prevent avoidable secondary claim delays and reduces repetitive payer follow-up.

OA-23 Adjustment Investigation

When OA-23 entries produce unexplained balances, the billing team can review the previous payer activity, secondary remittance, and posting records to determine whether the adjustment was interpreted correctly.

The objective is to separate legitimate prior-payer impact from new payments, contractual reductions, and actual reimbursement discrepancies.

Accounts Receivable Reconciliation

PROMBS helps practices investigate outstanding insurance balances, incorrect adjustments, and payment-posting inconsistencies that can make A/R reports unreliable.

This supports clearer financial reporting and more accurate follow-up priorities.

Secondary Insurance Denial Management

When a secondary claim contains a genuine denial or calculation discrepancy, PROMBS supports claim investigation, payer communication, appropriate corrections, and follow-up on reimbursement that may be legitimately due.

Learn more about our denial management services.

Revenue Cycle Performance Monitoring

Recurring payment and adjustment problems can be analyzed to identify weaknesses affecting claim accuracy, payment posting, and reimbursement.

Our revenue cycle management services support healthcare practices seeking more consistent insurance collections, accurate financial records, and reduced administrative workload.

Frequently Asked Questions About OA-23 Denial Code

What does denial code OA 23 mean?

OA-23 indicates the impact of adjudication by a previous insurance payer, including earlier payments and adjustments.

It is commonly used on secondary and tertiary remittances to communicate financial activity that has already affected the provider’s account.

Is OA-23 an actual claim denial?

Not necessarily. OA-23 is an adjustment code used to report prior-payer impact. It can appear on claims that receive secondary payment or are correctly adjudicated with no additional payment.

The complete remittance must be reviewed to determine whether a genuine denial exists.

How do you fix OA-23 in medical billing?

First, determine whether anything is actually wrong.

Review the primary and secondary EOBs or ERAs, verify previous payments and adjustments, confirm new secondary reimbursement, and reconcile final responsibility.

If the adjustment is correct, it generally requires no correction. If an actual posting or COB error exists, correct the underlying problem.

Should OA-23 be posted as a contractual adjustment?

OA-23 should not automatically be posted as a new contractual write-off.

It represents the impact of prior adjudication, and those amounts may already have been recorded.

Legitimate new contractual adjustments created by the secondary payer should be handled separately under the applicable adjustment codes and posting rules.

Why does OA-23 appear when secondary insurance pays zero?

A secondary payer may determine that no additional payment is due after considering previous insurance payment and its own benefit rules.

OA-23 may still appear because the remittance reports the impact of the earlier adjudication.

A zero-dollar payment is not automatically an incorrect denial.

What is the difference between OA-23 and CO-45?

OA-23 describes previous payer activity.

CO-45 generally identifies an applicable allowable or contractual reduction associated with the current adjudication.

A previous contractual adjustment should not be repeated as a new CO-45 adjustment simply because another payer processes the claim.

Can OA-23 create a credit balance?

OA-23 itself does not mean the practice received excess money.

However, incorrectly posting the OA-23 amount as another adjustment can create a false credit balance.

The account should be reconciled before any refund is considered.

Can OA-23 be billed to the patient?

No amount should be billed to the patient solely because it appears under OA-23.

Final patient responsibility must be established through the complete adjudication, applicable contracts, benefit rules, and patient billing protections.

Does Medicare use OA-23?

OA-23 may appear in Medicare Secondary Payer remittances when previous payer adjudication affects Medicare’s secondary payment processing.

It may also appear on remittances from other insurers that process claims after Medicare.

The code should be interpreted using the complete claim and remittance history.

Can OA-23 be appealed?

An OA-23 entry alone is not ordinarily a reason to appeal.

If the secondary insurer made an incorrect payment determination, the provider may need to request reprocessing, submit corrected COB information, or use an applicable reconsideration or appeal procedure.

The action should address the actual payer error rather than the mere presence of OA-23.

How can medical practices prevent OA-23 posting errors?

Practices can strengthen payment accuracy by verifying COB information, maintaining complete primary adjudication records, configuring ERA posting rules correctly, reconciling secondary payments, auditing negative balances, and investigating recurring adjustment patterns.

Does OA-23 always equal the primary insurance payment plus contractual adjustment?

No. That calculation may apply in straightforward examples, but it is not a universal formula.

X12 guidance explains that the amount depends on how previous payer activity affects the subsequent adjudication. Certain circumstances, including adjustments affected by a later payer’s payment, can change the reported prior-payer impact.

The complete remittance must be evaluated.

Final Takeaway: OA-23 Is About Accurate Reconciliation, Not Automatic Denial Recovery

An OA-23 adjustment should not be interpreted as an automatic insurance denial, another contractual write-off, or an amount that the patient must pay.

Its central purpose is to communicate how previous payer adjudication affects the current insurer’s remittance.

For medical practices, the financial risk arises when that information is misunderstood or incorrectly recorded.

Duplicate payment posting can distort insurance collections. Repeated contractual adjustments can create artificial credits. Incorrect coordination-of-benefits information can affect secondary reimbursement. Unverified patient balances can generate billing disputes.

These problems are preventable when the practice maintains an accurate financial history and reconciles every payer’s activity before finalizing the account.

The most reliable approach is:

Verify the primary payment → review OA-23 → validate secondary adjudication → post only new financial activity → confirm final responsibility → reconcile the account.

A well-managed secondary billing process does more than clear accounts receivable. It helps practices distinguish legitimate payment outcomes from recoverable discrepancies, protects against unnecessary refunds, improves reporting accuracy, and supports more dependable cash flow.