CO-23: Impact of Prior Payer Adjudication

What Does CO-23 Mean?

CO-23 is uncommon and may appear when the secondary payer applies a contractual adjustment based on the primary payer's adjudication rather than a standard administrative adjustment. This can occur when the secondary payer's contract specifically limits payment based on primary payer outcomes, or when the secondary determines a contractual write-off is appropriate given the primary's adjudication results.

When CARC 23 appears on a remittance, the secondary payer is telling you that their payment calculation was influenced by the primary payer's prior adjudication of the same claim. This code almost exclusively pairs with Group Code OA (Other Adjustment) because the adjustment is an administrative byproduct of the COB process — it is not a provider contractual issue or a patient responsibility determination at this stage.

The most common scenario is straightforward: the primary payer paid at or above the secondary payer's allowable rate, leaving nothing additional for the secondary to pay. The OA-23 adjustment reflects the difference between what the secondary would have paid independently and what the primary already covered. Less commonly, OA-23 surfaces when the primary payer made errors — underpayments, incorrect adjustments, or outright denials — that cascade into the secondary's adjudication. The secondary payer simply factors in the primary's outcomes when calculating their own payment.

Resolving OA-23 requires working backward through the primary payer's EOB. If the primary paid correctly and the secondary's adjustment math checks out, the remaining balance (if any) is the patient's responsibility. If the primary underpaid or erred, the fix starts there — you need to dispute with the primary payer first, and once the primary corrects their adjudication, the secondary will reprocess based on the updated primary EOB. Chasing the secondary payer for a higher payment is rarely productive when the root cause is the primary payer's adjudication.

How to Resolve

Audit the primary payer's EOB, verify the secondary's adjustment is mathematically correct, and address any primary payer errors before requesting secondary reprocessing.

1. Review primary EOB and secondary contract terms Compare the primary payer's adjudication against the secondary payer's contractual rules for calculating payment after primary adjudication.
2. Verify the CO adjustment is contractually correct Confirm the secondary payer's contractual write-off amount is consistent with your agreement. If not, contact the secondary payer for clarification or file a dispute.
3. Post the adjustment or dispute If the CO adjustment is correct, write off the amount. If incorrect, provide contract documentation and request reprocessing.

How to Prevent CO-23

• Understand how each secondary payer's contract calculates payments after primary adjudication
• Audit secondary EOBs against contract terms to ensure CO adjustments are being applied correctly
• Address primary payer underpayments before they cascade into incorrect secondary adjustments

Also Filed As

The same CARC 23 may appear with different Group Codes:

Related Denial Codes