Denial Codes

OA-23 Denial Code: Impact of Prior Payer Adjudication

What OA-23 means on a secondary remittance, how to post it, how the secondary claim carries the primary payer’s data, and when a $0 secondary payment needs a second look.

The OA-23 code means the payer adjusted the claim for what a prior payer already paid or adjusted. X12 defines reason code 23 as “The impact of prior payer(s) adjudication including payments and/or adjustments,” and restricts it to group code OA (Other Adjustment). It shows up on secondary and tertiary remittances, and most of the time it is bookkeeping, not a denial.

This page explains the official definition, why the amount is never a patient balance, how secondary claims carry the primary’s numbers, how to read a $0 secondary payment, and what to fix when OA-23 does hide a problem. More codes are in the denial codes guide.

Updated 2026-10-23. Reviewed by Jacob Greenberg, ClaimCarePro.

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What does OA-23 mean? The official X12 definition

OA-23 is group code OA with Claim Adjustment Reason Code 23. The X12 CARC list, read on October 23, 2026, gives code 23 as “The impact of prior payer(s) adjudication including payments and/or adjustments. (Use only with Group Code OA)”. It dates from January 1, 1995, last modified September 30, 2012 (x12.org).

In plain terms: before this payer looked at the claim, another payer (the primary) already paid part of it and adjusted part of it. The secondary uses OA-23 to take that portion off the table so its own payment applies only to what is left. The plain-English line we use in our own remittance review reads the same way: expected on a secondary or crossover remit, post as the prior-payer impact, no correction needed.

What the OA group code means for the patient balance

OA means Other Adjustment: the amount is neither a contractual write-off (CO) nor patient responsibility (PR), so an OA-23 amount is never billed to the patient. X12 says group codes “generally assign responsibility for the adjustment amounts,” and the OA-only rule on code 23 exists because the amount belongs to the prior payer’s adjudication, not to the provider or the patient.

What the patient owes after both payers is on the PR lines: deductible, coinsurance and copay. Under the NAIC Coordination of Benefits Model Regulation, the secondary plan also credits to its own deductible any amounts it would have credited without the other coverage, which is why the patient’s share on a secondary remittance can differ from the primary’s.

How a secondary claim carries the primary payer’s data

An electronic secondary claim (the 837P for professional claims) carries the primary payer’s results as data instead of a paper EOB. The claim names the other payer and the subscriber in the other-subscriber and other-payer loops (2320 and 2330), with the primary’s paid amount and its claim adjustment (CAS) group and reason codes; line-level results ride in the line adjudication loop (2430). The secondary reads those numbers, runs its own benefits, and reports the primary’s share back as OA-23.

For Medicare as the secondary payer, Noridian’s “Billing MSP Electronically” guide lists what has to come across from the primary remittance: the deductible amount, the coinsurance amount, the primary paid amount, and the obligated-to-accept amount when it applies. It also states the balancing rule: the paid amount in the line adjudication field plus the line-level adjustments must equal the total billed for that service line. It says Medicare does not need a copy of the primary’s remittance, and that Medicare tertiary claims must be submitted on paper.

Two practical consequences. First, copy the primary’s CAS codes as the primary sent them; do not translate them. Second, if the lines do not balance, the secondary rejects or denies the claim before it ever reaches OA-23.

How the secondary decides what to pay

Most commercial plans follow the NAIC model’s section 7: the secondary calculates what it would have paid with no other coverage, applies that to any allowable expense the primary left unpaid, and may reduce its payment so the total paid by all plans does not exceed the total allowable expense for the claim. Self-funded plans can use different methods (some pay only up to their own normal benefit), so the same claim can produce different secondary payments from different plans.

That is why a $0 secondary payment with only OA-23 is often correct. If the primary’s payment already met or exceeded what the secondary would have allowed, the secondary owes nothing, and the remaining patient share (if any) shows as PR.

Reading OA-23: normal or a problem?

How to read OA-23 on a secondary remittance
What you see	Likely reason	Action
Secondary pays the remainder	OA-23 for the primary’s impact, a payment, maybe PR for the patient’s share.	Normal. Post and move on.
Secondary pays $0, OA-23 only	Primary paid at or above what the secondary would allow.	Usually correct. Check the secondary’s allowed amount before writing off.
Secondary pays $0, OA-23 plus MA04 or N4	Primary data missing or not balancing.	Correct the other-payer data on the claim and resubmit.
Secondary pays twice what you expected	Primary paid amount was keyed low or left off.	Correct the claim and refund any overpayment the payer identifies.
CO-23 or PR-23 on the remit	Code 23 used outside its OA-only rule.	Call the payer before posting.

Remark codes (RARCs) that appear with OA-23

X12 does not assign remark codes to a reason code; each payer chooses. These active RARCs from the X12 RARC list (read October 23, 2026) are the ones you are most likely to see around a secondary or crossover claim:

Remark codes that commonly appear with OA-23
RARC	Official X12 text	What it means for you
MA18	“Alert: The claim information is also being forwarded to the patient’s supplemental insurer.”	Medicare crossed the claim over; do not send a duplicate to the supplemental plan until you check.
MA07	“Alert: The claim information has also been forwarded to Medicaid for review.”	The claim was forwarded to Medicaid.
MA04	“Secondary payment cannot be considered without the identity of or payment information from the primary payer.”	The primary data was missing; fix the secondary claim and resubmit.
N4	“Missing/Incomplete/Invalid prior Insurance Carrier(s) EOB.”	The primary data was incomplete or did not balance.

How to prevent OA-23 problems

Post the primary remittance fully (payment and every adjustment) before building the secondary claim.
Build secondary claims from the posted 835 data, not by retyping the EOB.
Check that every line balances: paid plus adjustments equals the line charge.
Confirm the payer order at every visit; CMS tells providers to bill the primary payer first.
Watch for crossover remark codes before sending anything to a supplemental plan.

When to hand secondary claims to someone else

Secondary balances are where money sits quietly: the primary paid, so the account looks handled, and the secondary never got a clean claim. ClaimCarePro’s denial management service reads every remittance by group, reason and remark code, separates normal OA-23 lines from the ones that hide a problem, corrects and resubmits secondary claims, and reports back weekly. Our team brings 30+ years of combined billing experience.

OA-23 questions, answered

What does denial code OA-23 mean?

OA-23 means the payer adjusted the claim because of what a prior payer already paid or adjusted. X12 defines reason code 23 as “The impact of prior payer(s) adjudication including payments and/or adjustments,” and says to use it only with group code OA. It appears on secondary and tertiary remittances.

Is OA-23 a denial?

Usually not. On most secondary remittances OA-23 is an accounting line: it removes the part of the charge the primary already handled, so the secondary’s payment applies only to the rest. It becomes a problem only when the secondary pays nothing and the reason is wrong primary data or a coordination mistake.

Can I bill the patient for an OA-23 amount?

No. The OA-23 amount represents money the primary payer paid or adjustments it took, so it is not patient responsibility. Anything the patient owes will appear on the remittances under the PR group (deductible, coinsurance or copay). Bill the patient from the PR lines.

Why did the secondary pay $0 with OA-23?

Most often because the primary already paid as much as or more than the secondary would have allowed. Under the NAIC model, a secondary plan may reduce its payment so the total paid by all plans does not exceed the total allowable expense. If the primary paid in full by the secondary’s measure, nothing is left for the secondary.

Why is it OA-23 and not CO-23 or PR-23?

Because X12 restricts reason code 23 to group code OA (Other Adjustment). A remittance showing CO-23 or PR-23 is using the code outside its definition. Call the payer and ask how it intended the adjustment, because the group code decides whether the amount is a write-off or a patient balance.

Do I need to send the primary EOB with a secondary claim?

It depends on the payer. Electronic secondary claims carry the primary payer’s paid amount and adjustments as data. For Medicare as secondary, the Noridian MSP guide says Medicare does not need a copy of the primary remittance. Some commercial payers still ask for the EOB; follow each payer’s instructions.

What is the difference between OA-23 and CO-22?

CO-22 is a denial from a payer that thinks another plan should pay first. OA-23 comes after the primary has paid, on the secondary’s remittance, showing the primary’s impact. If CO-22 started the coordination of benefits process, OA-23 is usually the sign it finished correctly.

How do I post OA-23 on a secondary remittance?

Post it as the prior-payer impact, not as a contractual write-off and not as a patient balance. The primary’s payment is already posted from the primary remittance, so the OA-23 line exists to keep the secondary’s math balanced. Then post the secondary’s payment and any PR amounts.

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