OA P4 denial code

Claim adjustment reason code P4. Often reported as OA P4 or CO P4.

Workers' comp claim found non-compensable

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 P4 means

The workers' compensation claim was decided to be non-compensable, so this carrier is not responsible for payment.

This is a workers' compensation code. It means the carrier made a formal decision that the claim is not compensable, so none of the treatment on it will be paid by this carrier.

This differs from P2, which focuses on whether the condition is work related. P4 covers a non-compensable decision on the claim as a whole. A rule reference may come with it on the remittance.

Group codes seen with P4

On a remittance, P4 comes after a group code. These are the ones it is most often reported with:

• OA P4 (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.
• CO P4 (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.

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 carrier denied the claim after investigating it.
• Filing or reporting requirements for the injury were not met.
• Coverage did not apply to the employer or employee on the injury date.

What to do next

1. Confirm the decision and whether it is under dispute with the carrier or the patient.
2. Bill the patient's health plan with the denial letter if the decision is final.
3. Track the dispute and rebill the carrier if the decision is overturned.

Related codes

• P2 (reason code) Not a work related injury or illness
• P8 (reason code) Claim under investigation
• P3 (reason code) Workers' comp settled: patient responsible