CO 243 denial code

Claim adjustment reason code 243. Often reported as CO 243.

Not authorized by network or PCP provider

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 243 means

The service was not approved by the network or the patient's primary care provider, as the plan requires.

Many managed care plans need the primary care provider or the network to refer or approve care first. This code says that approval was not in place for this service.

It replaced an older retired code along with code 242. Unlike 242, the provider may be in network; the gap is the missing referral or approval.

Group codes seen with 243

On a remittance, 243 comes after a group code. These are the ones it is most often reported with:

• CO 243 (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

• No referral from the patient's primary care provider was on file.
• A referral was issued to a different specialist or for a different service.
• The referral expired or ran out of visits before the service date.

What to do next

1. Check the payer portal for a referral covering this provider and date.
2. Ask the primary care office for a referral and whether a retro referral is allowed.
3. Resubmit with the referral number once it is in place.
4. Add a referral check to scheduling for plans that need one.

Related codes

• 242 (reason code) Not provided by a network or PCP provider
• 197 (reason code) No prior authorization on file
• 198 (reason code) Authorization limits exceeded