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CO-52 Denial Code (Deactivated): Provider Not Eligible

CO-52 meant the provider who referred, prescribed, ordered, or performed the service was not eligible to do so for this payer. X12 deactivated it; the three roles now have separate active codes: 183, 184, and 185.

X12 deactivated CARC52 on February 1, 2006. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Quick facts

Code
CO-52 (CARC 52)
Status
Deactivated StoppedFebruary 1, 2006 (in use since January 1, 1995).
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The provider side was responsible for the eligibility or enrollment problem, so the patient was not billed.
Official description
The referring/prescribing/rendering provider is not eligible to refer/prescribe/order/perform the service billed.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-52 meant

Every claim can involve several providers: someone who referred the patient, someone who ordered or prescribed the service, and someone who actually performed it. CARC 52 told you that one of them was not eligible, under the payer’s rules, to play that role for the billed service. It did not say which one.

That ambiguity made these denials slow to work, because the fix for an unenrolled ordering physician is very different from the fix for a rendering clinician whose credentialing is incomplete.

What replaced it

No replacement is named in the official text, but the current code set breaks it into role-specific codes:

  • CO-183 for the referring provider.
  • CO-184 for the prescribing or ordering provider.
  • CO-185 for the rendering provider.

CO-B7 is also used when the provider was not certified or eligible on the date of service.

If you still see CO-52

It should only turn up in legacy data or very old claim histories. When working such a claim, check each provider listed on it against the payer’s enrollment records for that date: NPI, taxonomy, enrollment effective dates, and any specialty restrictions on ordering. Once the enrollment gap is fixed, ask whether the payer allows retroactive effective dates, then resubmit or appeal. If the problem cannot be fixed for that date, the amount is generally a provider write-off.

  • CO-183 (The referring provider is not eligible to refer the service billed.): The referring provider is not eligible to refer the service billed.
  • CO-184 (The prescribing/ordering provider is not eligible to prescribe/order the service billed.): The prescribing or ordering provider is not eligible to prescribe or order the service.
  • CO-185 (The rendering provider is not eligible to perform the service billed.): The rendering provider is not eligible to perform the service billed.
  • CO-B7 (This provider was not certified/eligible to be paid for this procedure/service on this date of service.): The provider was not certified or eligible to be paid for this service on this date.

CO-52 FAQ

What usually causes a provider-eligibility denial?

Common reasons include a provider who is not enrolled with the payer, an enrollment that was not effective on the date of service, a lapsed license or certification, or an ordering provider whose specialty is not allowed to order that item.

Which new code matches my claim?

Identify which provider role the payer rejected. A referral problem maps to 183, an order or prescription problem to 184, and a problem with the person who performed the service to 185.