What Is OA 23 Denial Code in Medical Billing?
Official CARC 23 Definition
X12, the standards body that maintains Claim Adjustment Reason Codes, defines CARC 23 as the impact of prior payer(s) adjudication, including payments and/or adjustments, and attaches a usage note that it is to be used only with Group Code OA. The code lives in the same family as every other CARC on a 835 electronic remittance advice (ERA): a reason code, a group code and a dollar amount.
Meaning of the OA Group Code
Group codes indicate who is financially responsible for an adjustment. The main ones are:
- CO (Contractual Obligation): the provider is responsible, typically through a contract or payer rule.
- PR (Patient Responsibility): the amount can be billed to the patient or a subsequent payer.
- OA (Other Adjustment): used when neither CO nor PR applies.
- PI (Payer Initiated Reductions) and CR (Corrections and Reversals) cover other situations.
OA 23 is therefore not saying "the provider owes this" or "the patient owes this." It is saying "this amount reflects what happened at a previous payer."
How Prior Payer Adjudication Affects Claims
Under the X12 835 guidance, every claim in a remittance must account for 100 percent of the original submitted charge. A secondary payer therefore has to include the earlier payer’s payment and contractual reductions in its own math, otherwise the claim would not balance. CARC 23 is the label for that carried-over amount. The provider has already posted those items to the accounts receivable (AR) system from the primary remittance, so they should not be posted a second time.
Adjustment vs. Denial
A denial means a payer refuses payment for a reason such as lack of authorization or a non-covered service. An adjustment is any change between the billed amount and the paid amount, including contractual write-offs, patient cost-sharing and prior-payer impact. OA 23 belongs in the second category. It can appear on a claim that the secondary payer paid in full, paid in part or paid nothing, which is why the other lines on the remittance matter more than OA 23 itself.
How Does OA 23 Denial Code Work?
Primary Payer Adjudication
The first payer adjudicates the claim and reports its allowed amount, payment, patient responsibility and contractual adjustments on its own 835. Nothing in the OA 23 logic applies to that first payer, because no earlier payer exists.
Secondary Payer Processing
When the claim moves to the secondary payer, the billing system sends the primary payer’s payment and adjustment information on the secondary claim. The secondary payer calculates what it owes under its own rules, then reports a balanced remittance that carries the primary payer’s payment and contractual reductions as OA 23. Any additional contractual adjustment by the secondary payer is reported with a different reason code, and any remaining patient balance is reported under PR.
Tertiary Insurance Scenarios
With a third payer, the same logic repeats. The tertiary payer’s remittance carries the impact of both earlier payers under OA 23, and only the new payment, new contractual adjustments and new patient responsibility are reported as the tertiary payer’s own results.
Example of an OA 23 Adjustment (Illustration)
The figures below are simplified for illustration. Real payers use different benefit calculations.
| Step | Amount |
|---|---|
| Billed charge | $200.00 |
| Primary payer allowed amount | $120.00 |
| Primary payer paid | $96.00 |
| Primary contractual adjustment (CO) | $80.00 |
| Primary patient coinsurance (PR) | $24.00 |
| Secondary remittance: OA 23 amount (primary payment plus primary contractual adjustment) | $176.00 |
| Secondary payer paid | $18.00 |
| Remaining patient responsibility (PR) | $6.00 |
On the secondary remittance, $176.00 (OA 23) plus $18.00 paid plus $6.00 of patient responsibility equals the $200.00 charge. The $176.00 was already posted when the primary remittance was processed, so the biller posts only the new $18.00 payment and the $6.00 patient balance.
Common Causes of OA 23 Denial Code
Because OA 23 is mostly informational, the real question is usually not "what caused it" but "why is this claim going to a second payer, and do the numbers agree." These are the situations in which OA 23 appears.
- The primary insurance has already processed the claim. This is the standard case: the secondary claim is being adjudicated after the primary.
- The primary payment is reflected in secondary processing. The secondary payer includes the prior payment in its own calculation so the claim balances.
- Previous contractual adjustments affect the remaining balance. The write-off taken by the primary payer is carried forward and not repeated.
- Coordination of benefits rules shape what the secondary pays. Some secondary payers pay up to the patient’s remaining liability, others apply their own allowed amount or non-duplication rules.
- Prior payer adjustment information is included in claim reporting. The secondary claim itself must carry the primary payer’s payment and adjustment details, and errors there produce mismatches on the remittance.
It is worth looking harder when OA 23 appears on a claim that has no prior payer, which can point to other coverage on file with the payer that you were not aware of, or when the OA 23 amount does not match what you posted from the primary remittance.
How to Resolve OA 23 Denial Code
Verify Primary and Secondary Insurance Details
Confirm the order of coverage, policy numbers and effective dates. Incorrect insurance order is a common reason secondary claims behave unexpectedly. Eligibility verification that asks about other coverage at every visit, not only at registration, prevents many of these cases.
Review the Primary Payer EOB
Pull the primary payer’s EOB or 835 and note the allowed amount, payment, contractual adjustments and patient responsibility. These are the figures the secondary claim should carry.
Check Prior Payer Payments and Adjustments
Compare what the primary payer reported with what was entered on the secondary claim and with what was posted to the patient account. A mismatch is the most common reason an OA 23 amount looks wrong.
Review the Secondary Payer ERA
Read the whole remittance, not just OA 23. Look at the payment amount, the other reason codes, any patient responsibility and the remark codes. Those lines tell you whether the secondary payer paid, reduced or denied the claim.
Verify the 835 Transaction and CAS Details
In the 835 file, adjustments appear in CAS segments, which carry a group code, a reason code and an amount, and can appear at the claim or service-line level. Find the CAS segment that contains OA and 23, check its amount against the primary payer’s payment plus contractual adjustment, and confirm the claim payment amount in the CLP segment. A single CAS segment can carry several reason and amount pairs, so read all of them.
Reconcile Claim Balances
The charge should equal the sum of all payments and adjustments. If it does not, find the difference before posting. Do not repost prior payer amounts in order to force a balance, because that creates negative balances in AR.
Contact the Payer if the Adjustment Is Incorrect
If the secondary payer’s OA 23 amount does not match the primary remittance, first confirm that your own claim was submitted with the right primary payment and adjustment data. If it was, call the payer’s provider services, have the primary EOB ready, and request review. If your claim carried incorrect prior payer data, submit a corrected claim according to the payer’s requirements. Timely filing limits for secondary and corrected claims vary by payer, so check them before waiting.
OA 23 Denial Code Examples in Medical Billing
Example of a Secondary Insurance Claim
A patient has a commercial plan as primary and a spouse’s plan as secondary. After the primary pays, the biller submits the secondary claim. The secondary 835 shows OA 23 for the combined primary payment and contractual write-off, a small secondary payment, and a reduced patient balance. The correct action is to post the secondary payment, leave the OA 23 amount alone, and update the patient balance.
Example of Prior Payer Payment Adjustments
A Medicare patient has a supplemental plan. Medicare adjudicates first, and the claim crosses over to the supplement. The supplement’s remittance carries the Medicare payment and write-off as OA 23, and reports its own payment toward the Medicare deductible or coinsurance. The biller posts the supplemental payment and does not touch the OA 23 amount.
Example of an Incorrect Payment Reconciliation
The primary payer paid $84.00 after a payment correction, but the secondary claim was submitted with the original $96.00 payment. The secondary remittance’s OA 23 amount does not match the account, and the biller finds a $12.00 variance. The fix is to compare the primary 835 with the claim, submit a corrected secondary claim with the right figures, and confirm the account balance after reprocessing.
Is OA 23 a Denial or an Adjustment?
It is an adjustment. CMS and X12 documentation describe CARC 23 as a way to report the impact of prior payer adjudication, with Group Code OA, so that a secondary payer’s remittance can balance. In most cases it is informational and does not call for corrective action by itself.
Further investigation is needed when:
- The OA 23 amount does not equal what the earlier payer paid plus its contractual adjustment.
- OA 23 appears on a claim for which no prior payer was billed.
- The secondary payer paid nothing and the remaining reason codes are unclear.
- The account balance after posting does not reconcile.
Is OA 23 Patient Responsibility?
No. Patient responsibility is reported under the PR group code, such as deductible, coinsurance or copay adjustments. OA 23 is reported under OA. Billing a patient for an OA 23 amount is a mistake, because it often contains amounts that were already paid or already written off by the primary payer.
Patients should be billed only for the PR amounts on the final remittance, after all payers have processed the claim, and only in line with your contracts and applicable rules.
Difference Between OA 23 and Other Adjustment Codes
| Code | What it means | Who it affects | Typical action |
|---|---|---|---|
| OA 23 | Impact of prior payer(s) adjudication, including payments and adjustments | Informational for the provider’s AR | Do not repost; reconcile |
| CO 23 | Not consistent with the standard usage, which limits CARC 23 to Group Code OA | Unclear | Ask the payer to clarify |
| PR codes | Amounts the patient may owe (for example, deductible, coinsurance, copay) | Patient or a later payer | Bill according to final remittance |
| CARC 22 | Care may be covered by another payer per coordination of benefits | Claim sent to the wrong payer order | Fix COB and rebill the correct payer |
| CARC 45 | Charge exceeds the fee schedule, maximum allowable or contracted arrangement | Usually a contractual write-off | Post the contractual adjustment |
OA 23 vs. CO 23
X12’s usage note limits CARC 23 to Group Code OA. A CO 23 combination does not fit that rule, so treat it as something to question. Contact the payer or review your clearinghouse mapping before posting it as a write-off.
OA 23 vs. PR
PR amounts are billable to the patient or a later payer. OA 23 is not. They often appear together on the same remittance, so read each line instead of treating the whole claim as one outcome.
OA 23 vs. CARC 22
CARC 22 says another payer may be responsible for the care and is typically a coordination of benefits problem that requires correcting the insurance order or rebilling. OA 23 is not an error message. It reports that an earlier payer’s adjudication has already been applied.
OA 23 vs. CARC 45
CARC 45 reports a contractual reduction to the payer’s fee schedule, and X12’s usage note says it must not duplicate amounts already reported from prior payer adjudication. That is exactly the situation OA 23 covers. If the secondary payer’s own contract produces a new write-off, it appears under a separate reason code, not under 23.
How to Prevent OA 23-Related Billing Errors
- Verify insurance order. Check coverage at scheduling and at each visit. For Medicare beneficiaries, confirm Medicare Secondary Payer information.
- Maintain accurate COB information. Update patient records when coverage changes and respond to payer COB questionnaires promptly.
- Post primary payments correctly. Enter the payment, contractual adjustment and patient responsibility separately so the secondary claim carries accurate numbers.
- Reconcile secondary remittances. Compare each secondary 835 with the primary remittance before posting.
- Train billing staff. Make sure posters know that OA 23 is informational and that auto-posting rules do not write it off or bill it to the patient.
When these steps slip, balances age quietly in AR. Consistent accounts receivable follow-up and a structured denial management process help catch secondary claims that stall before they become write-offs.
How DocRev RCM Handles and Resolves OA 23-Related Billing Issues
At DocRev RCM, we understand that OA 23 adjustments are a common part of secondary insurance billing. Our medical billing team carefully reviews primary payer EOBs, verifies payment and adjustment details, and compares them with secondary payer remittances to identify discrepancies.
We follow a structured approach to:
- Verify primary and secondary insurance information.
- Review prior payer payments and contractual adjustments.
- Identify discrepancies in OA 23 amounts.
- Reconcile claim balances to prevent duplicate postings.
- Follow up with payers and submit corrected claims when necessary.
By maintaining accurate payment records and closely monitoring secondary claims, DocRev RCM helps prevent billing errors, improve claim reconciliation, and support a healthier revenue cycle for healthcare providers.
Need reliable medical billing support? Connect with DocRev RCM to learn how we manage complex billing challenges.
Frequently Asked Questions About OA 23
What does OA 23 mean in medical billing?
It means the payer is reporting the impact of a prior payer’s payment and adjustments on this claim, under the Other Adjustment group code.
Is OA 23 a denial code?
Generally no. It is an adjustment that appears on secondary or later remittances to make the claim balance. Look at the other codes on the remittance to see whether the claim was paid or denied.
Can OA 23 be appealed?
OA 23 on its own is not usually something to appeal. If the secondary payer paid less than expected or denied the claim, appeal based on the other reason codes. If the prior payer’s adjudication was wrong, address it with that payer first.
Does OA 23 mean the patient owes money?
No. Patient responsibility is reported with PR. Bill the patient only for PR amounts on the final remittance.
Why does OA 23 appear on an ERA?
Because a secondary or later payer needs to account for the full original charge, including what earlier payers paid and adjusted, in its electronic remittance advice.
How should medical billers handle OA 23?
Treat it as informational: do not repost prior payer amounts, verify that the amount matches the primary remittance, post any new payment and adjustments, and reconcile the balance.
What is the difference between OA 23 and CO 23?
OA 23 follows the standard usage. CO 23 does not match the X12 note limiting CARC 23 to Group Code OA, so confirm with the payer before acting on it.
Conclusion
OA 23 is a bookkeeping signal, not usually a problem. It tells you a prior payer’s payment and adjustments were applied so the secondary remittance balances. The practical takeaway is to read the whole ERA, avoid reposting prior payer amounts, never bill the patient for OA 23, and investigate only when the numbers do not reconcile. If secondary claims and COB follow-up are slowing your cash flow, talk to a DocRev Rcm billing specialist.