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CO-279 Denial Code: Not in Preferred or Narrow Network

CO-279 means the services weren't provided by a preferred network provider for this member. The provider may be contracted with the payer, but not in the member's narrow or tiered network, so the plan reduces or denies benefits.

Quick facts

Code
CO-279 (CARC 279)
Status
Active In use since November 1, 2016; last modified July 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The provider absorbs the amount, typically because its contract limits billing the patient. Don't bill the patient under CO.
  • PR (Patient Responsibility): Used when the member is responsible for choosing a non-preferred provider, often through higher cost-sharing. Check your contract and applicable law before billing.
Official description
Services not provided by Preferred network providers. Usage: Use this code when there are member network limitations. For example, using contracted providers not in the member's 'narrow' network.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-279 means

CARC 279 says services not provided by preferred network providers. The official usage note explains when to use it: when there are member network limitations, such as a contracted provider who isn’t in the member’s narrow network.

That’s the key distinction from a general out-of-network denial like CO-242. With CO-279, you may well have a contract with the payer. The problem is that this member’s plan uses a smaller, preferred, or tiered network, and your practice isn’t in it. Payers offer these products to lower premiums, and they limit which contracted providers members can see at full benefits.

Depending on the plan, the result can be a denial, a lower benefit tier with higher patient cost-sharing, or a reduced allowed amount.

Common causes

  • Member enrolled in a narrow network product that doesn’t include your practice.
  • Tiered network plans where your practice is in a lower tier.
  • Contract doesn’t list the product, even though you’re in the payer’s broad network.
  • Provider or location not loaded into the preferred network, despite being eligible.
  • Patient changed plans to a narrow network product at open enrollment.

How to fix it

  1. Check the member’s plan and network name from the card and eligibility response.
  2. Review your contract for the products and networks it covers.
  3. If you should be in the network, ask your provider representative to fix the network loading and reprocess affected claims.
  4. If you aren’t, consider appealing for an exception where the member had no access to a network provider, or where care was urgent.
  5. Bill the patient only for PR amounts allowed under your contract and law.
  6. For future visits, tell the patient about the network limitation or help them find a network provider.

How to prevent it

  • Verify the member’s specific network during eligibility checks, not just the payer name.
  • Keep a list of products and tiers your contracts include.
  • Confirm network loading for new providers and locations.
  • Recheck network status after open enrollment. See provider enrollment denials and eligibility and COB denials.

Remark codes that may appear with CO-279

  • N130 (Consult plan benefit documents/guidelines for information about restrictions for this service.): Points to plan documents describing the member's network limitations.
  • N52 (Patient not enrolled in the billing provider's managed care plan on the date of service.): The patient wasn't enrolled in the billing provider's managed care plan on the date of service.
  • CO-242 (Services not provided by network/primary care providers.): Services not provided by network or primary care providers, a general out-of-network denial.
  • CO-243 (Services not authorized by network/primary care providers.): Services not authorized by network or primary care providers.
  • CO-P24 (Payment adjusted based on Preferred Provider Organization (PPO).): Payment adjusted based on a PPO, used in property and casualty claims.
  • CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): Fee schedule reduction, which may differ between network tiers.

CO-279 FAQ

What is a narrow network?

A plan network that includes only a subset of the payer's contracted providers, often to lower premiums. A provider can be contracted with the payer overall but excluded from a specific narrow network product.

Why was I denied if I'm contracted with the payer?

Your contract may not include the member's specific product or tier. The official usage note says this code applies to member network limitations, for example contracted providers not in the member's narrow network.

What should I do after CO-279?

Confirm which products and tiers your contract covers, check the member's plan, and ask the payer to reprocess if you're in the right network. If you're not, discuss options with the patient for future care.

Can I bill the patient?

Only if the payer reports PR and your contract and applicable balance-billing laws allow it.