Skip to main content

CO-183 Denial Code: Referring Provider Not Eligible

CO-183 means the referring provider listed on the claim is not eligible to refer the service billed. Usually the referring NPI isn't enrolled with the payer, is an ineligible provider type, or was entered incorrectly in box 17 and 17b.

Quick facts

Code
CO-183 (CARC 183)
Status
Active In use since June 30, 2005; last modified July 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The billing provider absorbs the amount. The patient isn't responsible for a referral eligibility problem.
Official description
The referring provider is not eligible to refer the service billed. Usage: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-183 means

CARC 183 reads “The referring provider is not eligible to refer the service billed.” Some services are payable only when referred by an eligible provider. The payer checked the referring provider on the claim and found a problem: they aren’t enrolled, they’re a provider type that can’t refer this service, or the name and NPI don’t match its records.

The usage note refers to the 835 Healthcare Policy Identification segment (loop 2110 REF), which may identify the policy defining eligible referrers.

Example: a specialist bills a consult with a referring provider in box 17b who is a newly hired clinician not yet enrolled with the payer. The claim is denied CO-183 with remark N574 or a similar referring-provider remark.

Common causes

  • Referring provider not enrolled with the payer (or, for Medicare, not in PECOS with an eligible status).
  • Ineligible provider type for referring the service under payer rules.
  • Group NPI in box 17b instead of the individual NPI.
  • Name mismatch between box 17 and the payer’s record.
  • Wrong qualifier in box 17 (for example DN vs. DK).
  • Referring provider’s enrollment lapsed or was revoked.
  • A resident, intern, or other trainee listed as the referring provider when the payer requires the supervising teaching physician instead.
  • Referral from outside the plan’s network where the plan requires in-network referrers.

How to fix it

  1. Check box 17 and 17b for the name, qualifier, and individual NPI.
  2. Verify enrollment of the referring provider with the payer, or in Medicare’s ordering and referring lookup.
  3. If the data was wrong, submit a corrected claim with resubmission code 7.
  4. If the referrer isn’t enrolled, ask them to enroll, or obtain a referral from an eligible provider, following payer rules on timing.
  5. Appeal if the referrer was eligible on the date of service and the payer’s records were wrong.

How to prevent it

  • Capture referring provider NPI at scheduling and verify it against the payer’s enrollment tools.
  • Keep a directory of frequent referral sources with confirmed enrollment status.
  • Enforce individual NPIs in box 17b in your billing system.
  • Watch for referring provider denials by source to find referrers needing enrollment help. See referral denials.

Remark codes that may appear with CO-183

  • N574 (Our records indicate the ordering/referring provider is of a type/specialty that cannot order or refer.): The referring provider's type or specialty cannot refer or order.
  • N575 (Mismatch between the submitted ordering/referring provider name and the ordering/referring provider name stored in our records.): The referring provider's name doesn't match the payer's records.
  • N286 (Missing/incomplete/invalid referring provider primary identifier.): The referring provider's NPI is missing or invalid.
  • N754 (Missing/incomplete/invalid Referring Provider or Other Source Qualifier on the 1500 Claim Form.): The qualifier in box 17 is missing or invalid.
  • CO-184 (The prescribing/ordering provider is not eligible to prescribe/order the service billed.): The ordering or prescribing provider, rather than the referring provider, isn't eligible.
  • CO-185 (The rendering provider is not eligible to perform the service billed.): The rendering provider isn't eligible to perform the service.
  • CO-197 (Precertification/authorization/notification/pre-treatment absent.): Authorization or referral was absent altogether.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Missing information, such as a blank referring NPI, rather than an ineligible one.

CO-183 FAQ

Why does the referring provider's enrollment affect my payment?

Some payers, including Medicare for certain services, only pay when the referring or ordering provider is enrolled and of an eligible type. Your claim depends on their status even though you rendered the service.

What goes in box 17?

The referring provider's name with a qualifier (DN for referring, DK for ordering, DQ for supervising) and their NPI in 17b. Use the individual's NPI, not a group NPI.

Can I just remove the referring provider?

Only if the service doesn't require one under the payer's rules. If a referral is required, removing it will likely produce a different denial.

Can I bill the patient for CO-183?

No. The CO group code makes it the provider's responsibility. Work with the referring provider's office to resolve their enrollment or data instead.