What does denial code CO-183 mean?

CO-183 means the provider named as the referral source on the claim is not eligible to refer that service with this payer. Usually they are not enrolled, their enrollment lapsed, or the identifier submitted was wrong or belonged to a group instead of an individual.

Why am I denied for another provider's enrollment problem?

Because the payer holds the billing provider responsible for the accuracy of the referral information on the claim. It is a real burden, which is why validating referring provider identifiers at intake is worth more than working these denials afterwards.

CO-183: The referring provider is not eligible to refer this service

CO-183 punishes the billing provider for someone else's enrollment status, which is what makes it frustrating and also what makes it preventable. The service and the coding may be flawless; the referring provider on the claim is simply not someone the payer will accept as a referral source, whether because they are not enrolled, their enrollment lapsed, or their provider type cannot refer. Diagnostic and specialist claims carry most of this volume because they carry a referring provider most often.

What it means: The provider identified as the referral source is not enrolled or not eligible with this payer to refer the service billed.
Who pays the balance: Contractual - verifying the referring provider's eligibility is the billing provider's responsibility.
Group code CO: Contractual Obligation - the provider absorbs the balance and cannot bill the patient

Why CO-183 happens

The referring provider is not enrolled with the payer, or their enrollment lapsed.
The referring provider's identifier on the claim is wrong, belongs to a group rather than an individual, or is missing a digit.
The referring provider's type is not permitted to refer this particular service under the payer's rules.
A resident or non-credentialed clinician was listed as the referral source instead of the supervising physician.
The referral came from inside the same group and the ordering provider field was populated with an ineligible internal identifier.

How to fix a CO-183 denial

1
Verify the referring provider's identifier and enrollment
Check the identifier against the national registry and confirm active enrollment with this specific payer. A valid identifier is not the same as an enrolled one, and the payer only accepts the latter.
2
Confirm the right individual is named
The referring provider has to be the individual clinician, not the group. A group identifier in an individual field fails the eligibility check even when the group is enrolled.
3
Substitute the supervising physician where a resident referred
If the referral originated with a resident or a non-credentialed clinician, the supervising physician is typically the correct referral source and the claim can be corrected accordingly.
4
Resubmit as a corrected claim once verified
Correct the referring provider field and resubmit. If the referring provider genuinely cannot be made eligible, the referral itself needs to come from someone who can, going forward.

Preventing CO-183 denials

Validate referring provider identifiers against the national registry at intake rather than accepting whatever arrives on the referral.
Keep a verified list of frequent referral sources with their enrollment status per payer, refreshed periodically.
Default the referring provider field to the supervising physician when the referral originates from a resident.

CO-183 frequently asked questions

What does denial code CO-183 mean?: CO-183 means the provider named as the referral source on the claim is not eligible to refer that service with this payer. Usually they are not enrolled, their enrollment lapsed, or the identifier submitted was wrong or belonged to a group instead of an individual.
Why am I denied for another provider's enrollment problem?: Because the payer holds the billing provider responsible for the accuracy of the referral information on the claim. It is a real burden, which is why validating referring provider identifiers at intake is worth more than working these denials afterwards.

Related denial codes

CO-185 CO-170 CO-16 CO-8

Last reviewed August 5, 2026.

Denial code explanations are original plain-English summaries written for reference and are not the official X12 code descriptions. Payer handling of any code varies by contract - always verify against the remittance advice and your payer agreement before adjusting a claim.