CO 279 denial code

Claim adjustment reason code 279. Often reported as CO 279 or PR 279.

Out of the member's preferred network

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 279 means

The member's plan limits benefits to a preferred or narrow network, and the services came from providers outside it.

Plans with narrow or tiered networks may cover care only from certain providers. This code says your services were outside the network the member is restricted to, even if you are contracted with the payer for other products.

Any remark codes on the line may say which network applied. Who owns the balance depends on the group code and any network exceptions.

Group codes seen with 279

On a remittance, 279 comes after a group code. These are the ones it is most often reported with:

• CO 279 (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 279 (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 member is in a narrow network product that does not include the provider.
• The provider is in the payer's broad network but not the member's specific product network.
• No referral or exception was obtained for out of network care.

What to do next

1. Verify which network product the member is enrolled in and your status in it.
2. Check whether an exception applies, such as emergency care or no in network option.
3. Appeal with support for the exception, or follow the contract and group code before billing the patient.

Related codes

• 96 (reason code) Service not covered by the plan
• 197 (reason code) No prior authorization on file