CO P1 denial code

Claim adjustment reason code P1. Often reported as CO P1 or OA P1.

State rule drove the adjustment

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 P1 means

On a property and casualty claim, the adjustment comes from a state requirement, with the details in a remark code.

P1 flags that a state rule, rather than a plan or contract term, drove the adjustment on a property and casualty claim, such as workers' compensation or auto medical.

The reason code alone does not say which rule applied. The payer is expected to explain it in a claim payment remark code, so read that before deciding whether to correct, appeal or accept the adjustment.

Group codes seen with P1

On a remittance, P1 comes after a group code. These are the ones it is most often reported with:

• CO P1 (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 P1 (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

• A state fee, billing or documentation requirement for property and casualty claims was not met.
• The claim was adjusted to comply with a state mandate on how the service is paid.
• Required state forms or data were missing from the claim.

What to do next

1. Read the remark code sent with P1 to identify the state requirement involved.
2. Check the state's property and casualty or workers' compensation billing rules for that requirement.
3. Correct and resubmit if the claim missed required state data or forms.
4. Dispute through the state process if you believe the requirement was applied wrongly.

Related codes

• P12 (reason code) Workers' comp fee schedule adjustment
• P13 (reason code) Reduced under workers' comp rules
• 16 (reason code) Missing information or billing error