OA-23 denial code: causes, meaning and how to resolve it

An OA-23 adjustment can be confusing because the claim may look as though it has already been handled correctly. The primary payer processed the service, the secondary claim was sent, and then the remittance returns with OA-23 instead of the payment the billing team expected.

The wrong first move is to treat it like a generic coding denial. OA-23 points back to what a prior payer already did with the claim. Resolution starts by reviewing that earlier adjudication, confirming the payer order, and checking whether the secondary payer received the correct payment and adjustment information.

What does the OA-23 denial code mean?

CARC 23 is used when a payer adjusts a claim because of the impact of prior payer adjudication, including payments and/or adjustments. CMS remittance guidance publishes the CARC 23 narrative as: “The impact of prior payer(s) adjudication including payments and/or adjustments.” It is used with group code OA.

OA means Other Adjustments. That matters because OA-23 does not automatically mean the prior payer paid the claim in full, and it does not by itself establish patient responsibility. The primary payer may have paid part of the claim, applied adjustments, assigned patient responsibility, or made another adjudication decision that changed what the secondary payer considered payable.

People often search for “OA 23 denial” or “OA 23 denial reason,” but CARC 23 is technically an adjustment reason. It can still leave the provider with an unpaid or underpaid balance that needs review.

Why prior payer adjudication matters

OA-23 commonly appears in coordination-of-benefits situations. When a patient has more than one health plan, the plans must determine which payer is primary and what the secondary payer should consider after the first payer processes the claim. CMS describes coordination of benefits as the process used to determine payment responsibilities when more than one plan covers the patient.

The secondary payer therefore needs accurate information from the primary adjudication. If payment amounts, patient responsibility, contractual adjustments, or other primary-payer details are missing or transmitted incorrectly, the secondary payment may not match what the provider expected. Under Medicare Secondary Payer rules, providers must determine whether another plan has primary payment responsibility before billing Medicare.

Common causes of an OA-23 adjustment

The same OA-23 adjustment code can appear for several operational reasons. Common examples include:

• The primary payer made a payment or adjustment that legitimately reduces what the secondary payer owes.
• The secondary claim was submitted without complete prior-payer adjudication details.
• The payer order is wrong because coordination-of-benefits information is outdated or incomplete.
• The primary EOB or ERA does not match the information sent on the secondary claim.
• A crossover or electronic secondary claim carried incomplete or incorrectly mapped adjustment data.

The important point is that CARC 23 does not automatically identify a diagnosis, authorization, medical necessity, or timely-filing problem. The first review should focus on the earlier payer decision and the information used by the next payer.

How to resolve an OA-23 denial or adjustment

A consistent review sequence is more effective than repeatedly correcting and resubmitting the claim:

1. Review the current ERA or EOB. Confirm the payer, service line, OA-23 amount, and any related CARCs or RARCs.
2. Pull the prior payer adjudication. Compare the primary payer’s allowed amount, payment, adjustments, and patient responsibility with what was transmitted to the secondary payer.
3. Verify the payer order and COB record. Make sure the correct plan was billed first and coverage information is current for the date of service.
4. Compare the secondary claim with the primary EOB or ERA. Look for missing prior-payment amounts, service-line mismatches, incorrect adjustment mapping, or a claim sent before primary adjudication was complete.
5. Correct only the issue you find. The next action may be a corrected claim, COB update, primary-payer documentation, reconsideration, or appeal. If the secondary payer calculated the claim correctly, an appeal may not be appropriate.

This is where structured denial management helps. The team should be able to distinguish a valid secondary adjustment from a payer error before deciding whether to resubmit, appeal, or close the balance.

What not to do when OA-23 appears

Do not automatically move the remaining balance to the patient. OA is the Other Adjustments group code, not PR, or Patient Responsibility. The full remittance, benefit information, contract terms, and payer rules need to support patient liability before a balance is transferred.

Also avoid sending the same claim again without changing the underlying information. If incomplete prior-payer data caused the problem, the same submission is likely to produce the same result. Likewise, changing coding simply because the claim did not pay can create a new error when the original coding was correct.

How to prevent repeat OA-23 problems

Prevention starts with cleaner coordination-of-benefits data. Registration and eligibility workflows should identify other active coverage, confirm payer order when possible, and update changes before billing. Secondary claims should carry the prior payer information required for adjudication, and teams should have a standard way to compare secondary remittances with the original EOB or ERA when payment does not reconcile.

Recurring OA-23 patterns should also be reviewed by payer. If one payer repeatedly returns OA-23 because a particular adjustment is mapped incorrectly, that may be a system or workflow problem rather than a series of unrelated denials. A payer-specific denial management workflow can help turn repeated adjustment patterns into a permanent correction.

How RCMGen approaches OA-23 denial resolution

At RCMGen, OA-23 is reviewed first as a payment-sequencing and remittance-reconciliation issue. The team checks the current remittance, prior payer adjudication, COB information, claim history, and related payer messages to understand why the claim was adjusted.

That review sits inside the broader revenue cycle management workflow. When the root cause is registration or eligibility, feedback goes upstream. When the secondary claim is incomplete, the billing workflow is corrected. When the payer appears to have applied the prior adjudication incorrectly, the claim can move to reconsideration or appeal with supporting documentation.

Frequently asked questions about OA-23