CO 39 denial code

Claim adjustment reason code 39. Often reported as CO 39 or PR 39.

Authorization was requested and denied

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 39 means

The payer had already turned down the authorization or precertification request for this service.

Someone asked the payer to approve the service in advance, and the payer said no. The claim was then denied because the service went ahead without approval.

It differs from a missing authorization: here there is a recorded denial. Overturning it usually means appealing the authorization decision with clinical support. The patient's financial responsibility depends on the group code and any waiver signed.

Group codes seen with 39

On a remittance, 39 comes after a group code. These are the ones it is most often reported with:

• CO 39 (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 39 (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.

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 denied the precertification as not medically necessary.
• The authorization request lacked clinical documentation, and the payer denied it.
• The service was scheduled before the payer finished reviewing the request, and the review ended in a denial.

What to do next

1. Pull the authorization denial letter and note the stated reason.
2. Appeal the authorization decision with clinical records and a letter of medical necessity if the payer allows it.
3. Check whether a peer to peer review is still possible.
4. Check for a signed patient waiver before moving any balance to the patient.

Related codes

• 50 (reason code) Not medically necessary per the payer
• 197 (reason code) No prior authorization on file
• 40 (reason code) Did not meet emergency or urgent criteria