CO A1 denial code

Claim adjustment reason code A1. Often reported as CO A1, PR A1 or OA A1.

General denial, see remark code

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 A1 means

A general denial: the payer refused the claim or line and relies on an attached remark code to say why.

A1 is a catch-all. Payers are expected to use it only when no more specific reason code fits, and it should always come with at least one remark code (or, on pharmacy claims, an NCPDP reject code) that carries the real reason.

Because the reason code itself says almost nothing, the remark code is what you work from. If the remittance shows A1 with no remark code, you usually need to call the payer or check their portal to learn the actual cause.

Group codes seen with A1

On a remittance, A1 comes after a group code. These are the ones it is most often reported with:

• CO A1 (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.
• PR A1 (Patient Responsibility): The amount is assigned to the patient. Deductibles, coinsurance and copays are the everyday examples. Whether you can collect it still depends on your contract and the patient's plan.
• OA A1 (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 payer's reason did not match any specific adjustment code, so it used the general denial with a remark code.
• Payer system edits that are specific to a plan or program produced the denial.
• The claim failed an eligibility, coverage or documentation rule that the remark code explains.

What to do next

1. Read every remark code reported with A1 on the claim and line level before taking action.
2. Contact the payer or use its portal if no remark code was sent, and record the reason given.
3. Correct and resubmit the claim if the remark code points to a billing error.
4. Appeal with supporting records if you believe the service was covered and billed correctly.

Related codes

• N130 (remark code) Check plan benefits for restrictions
• 16 (reason code) Missing information or billing error
• 96 (reason code) Service not covered by the plan