CO P16 denial code

Claim adjustment reason code P16. Often reported as CO P16 or OA P16.

Provider not authorized for workers' comp

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 P16 means

The workers' compensation payer says the provider is not authorized or certified to treat injured workers in this jurisdiction.

This is a workers' compensation code. Some jurisdictions require providers to register, be certified or be part of an approved network before treating injured workers. P16 means the payer found the provider did not meet that requirement.

It is used with group code CO or OA.

Group codes seen with P16

On a remittance, P16 comes after a group code. These are the ones it is most often reported with:

• CO P16 (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 P16 (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 provider has not registered or been certified with the jurisdiction's program.
• The provider is outside the approved network the employer uses.
• The certification lapsed before the date of service.

What to do next

1. Check the provider's registration or certification status for the jurisdiction.
2. Complete the registration or network enrollment if it is missing.
3. Appeal if the provider was authorized on the date of service, with proof attached.

Related codes

• P25 (reason code) Adjusted under a medical provider network
• B7 (reason code) Provider not certified for the service
• P17 (reason code) Referral not authorized by attending