CO 22 denial code

Claim adjustment reason code 22. Often reported as CO 22 or OA 22.

Another payer may be primary

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 22 means

The payer thinks another insurance plan should pay first under coordination of benefits, so it did not pay as primary.

The payer's records show, or suggest, that the patient has other coverage that comes first under coordination of benefits rules. It will not pay as primary until that is sorted out.

This is often an out-of-date coordination record rather than a real second plan. The patient may need to confirm their other coverage with the plan before it will reprocess. It is usually CO, sometimes OA.

Group codes seen with 22

On a remittance, 22 comes after a group code. These are the ones it is most often reported with:

• CO 22 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.
• OA 22 (Other Adjustment): Used for adjustments that are neither the provider's contractual write-off nor the patient's share. It often appears with coordination of benefits, for example when another payer already paid.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The patient has another active plan, such as an employer plan or a spouse's plan, that is primary.
• The payer's coordination of benefits record is outdated and still lists coverage that has ended.
• The patient has Medicare or another government program that the payer's rules treat as primary.
• The claim did not include the primary payer's payment information when it was billed as secondary.

What to do next

1. Ask the patient about all current coverage and check eligibility with every plan they name.
2. Bill the correct primary payer first, then send the secondary claim with the primary's payment data.
3. If there is no other coverage, have the patient update their coordination of benefits record with the plan.
4. Ask the payer to reprocess the claim once its coordination record is updated.

Related codes

• 23 (reason code) Prior payer payment affected this claim
• 16 (reason code) Missing information or billing error
• 109 (reason code) Not covered by this payer, send elsewhere