CO-183 means the payer looked at the referring provider on the claim and decided that person can’t refer this service. The service itself may be covered, and the rendering provider may be fine. The problem sits in the referral field. Usually the referrer isn’t enrolled with the payer, is a provider type the payer won’t accept as a referrer, or the claim names the wrong person. (Primary source: X12 Claim Adjustment Reason Codes)
In brief: CARC 183 reads “The referring provider is not eligible to refer the service billed.” Find out who really referred the patient, check that provider’s enrollment and type, and correct Box 17 / 17b on the CMS-1500 (or FL 78 with qualifier DN on the UB-04). If the referrer truly can’t refer, get a referral from someone who can.
Part of our denial codes library. Written by Manikandan J, CPC, CRCR, who has worked referral and enrollment denials for imaging and specialty groups. Published 22 October 2026. Last updated: 22 October 2026. Code wording quoted word for word from X12.
Official CARC 183 description
| Field | X12 text |
|---|---|
| Code | 183 |
| Description | “The referring provider is not eligible to refer the service billed.” |
| X12 usage note | Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present. |
| Start | 06/30/2005 |
| Last modified | 07/01/2017 |
Source: X12 Claim Adjustment Reason Codes, checked 22 October 2026.
With group code CO, the provider absorbs the amount unless the claim is fixed. Don’t bill the patient for a CO-183 line.
Example scenario (fictional names), part 1
CO-183 Denial Example: What Happened
Priya Natarajan runs billing for Lakeshore Imaging Partners. A patient came in for a lumbar spine MRI without contrast (72148) for low back pain with radiculopathy (M54.16). The intake sheet listed the patient’s chiropractor as the referring provider, so Box 17 showed DN with the chiropractor’s name and NPI. The claim went to Silverpine Health Plan, a fictional commercial plan.
The 835 came back with CAS*CO*183 on the 72148 line and remark LQ*HE*N574, “Our records indicate the ordering/referring provider is of a type/specialty that cannot order or refer.”
Was the scan really unpayable, or was the wrong name in Box 17? Keep reading, or jump to how the CO-183 denial was resolved.
Why payers deny with reason code 183
Payers keep a list of who may refer for each type of service. CARC 183 fires when the referrer on the claim isn’t on that list for the code billed. Common triggers:
- Provider type limits. Some plans don’t accept chiropractors, physical therapists or other non-physician types as referrers for advanced imaging or specialist visits.
- Not enrolled. The referring provider has no active enrollment or registration with the payer. Medicare, for example, checks referrers against its Order and Referring file.
- Wrong person captured. Front-desk intake records who sent the patient, not who signed the referral or order.
- Opted-out or excluded referrer. A provider who has left the network or been excluded can’t refer for covered services.
Denial code 183 vs similar referral codes
| Code | What it says | Main difference |
|---|---|---|
| CO-183 | Referrer not eligible to refer the service | The person is the problem |
| CO-184 | Prescribing/ordering provider not eligible | Ordering, not referring |
| CO-197 | Precertification/authorization absent | No auth on file |
| CO-16 | Claim lacks information | Missing data, not eligibility |
How to fix a CO-183 denial
- Read the remark code. N574 points to provider type. N575 points to a name mismatch, so the fix is a spelling or record correction.
- Find the real referral. Pull the signed referral or order from the chart. The person who signed it belongs in Box 17, not the person the patient mentioned at check-in.
- Check the referrer’s status. Look up the NPI in the NPPES NPI Registry and confirm enrollment with the payer.
- Correct Box 17 and 17b. Use qualifier DN for a referring provider. Enter the name as it appears in NPPES and the referrer’s individual NPI.
- Send a corrected claim with frequency code 7 and the original claim number in Box 22.
- No eligible referrer? Ask the patient’s physician for a referral if the plan allows one after the fact. If not, follow the plan’s appeal steps or treat the line as a write-off.
Example scenario (fictional names), part 2
How the CO-183 Denial Was Resolved
Priya opened the chart. The chiropractor had sent the patient to the primary care physician. The physician, Dr. Helen Brandt, signed the MRI order two days later. Intake had copied the chiropractor’s name from the patient’s form, and Silverpine doesn’t accept chiropractors as referrers for MRI.
Fix: Priya sent a corrected claim with Box 22 code 7 and the original claim number. Box 17 now showed DN with Dr. Brandt’s name, and Box 17b her individual NPI.
Outcome: Silverpine reprocessed the 72148 line and paid it. Lakeshore changed intake so staff copy the referrer from the signed order, never from the patient’s form.
Names and details are illustrative; no real patient data.
- Box 17 / FL 78: referrer changed from the chiropractor named at intake to Dr. Helen Brandt, who signed the MRI order (qualifier DN on both forms).
- Box 17b / FL 78 NPI: her individual NPI (placeholder 1234567890).
- Box 22 / FL 4 + FL 64: resubmission code 7 with the original claim number (type of bill 0137 on the UB-04).
- Box 24D / FL 44: 72148 with M54.16 (entered as M5416) is unchanged.
Where the referring provider goes on each claim form
| Claim | Field | What to enter |
|---|---|---|
| CMS-1500 | Box 17 | Qualifier DN (referring) or DK (ordering), then the provider’s name |
| CMS-1500 | Box 17b | Referring provider’s individual NPI |
| UB-04 | FL 78 or 79 | Qualifier DN, the referrer’s NPI and name |
| 837P / 837I | Loop 2310A | Referring provider name and NPI |
The NUCC 1500 instructions explain Box 17 qualifiers in detail.
Prevention checklist
- Copy the referrer from the signed referral or order, never from intake notes.
- Keep a list of provider types each major payer won’t accept as referrers.
- Check new referrers against NPPES before the first claim.
- Set a scrubber edit for advanced imaging with a non-physician referrer.
Recap
CO-183 means the payer won’t accept the person in the referring provider field for this service. Pull the signed referral, confirm the referrer’s type and enrollment, then correct Box 17 / 17b or FL 78 and send a corrected claim. If no eligible provider referred the patient, get a valid referral or appeal under the plan’s rules.
FAQ
What does denial code CO-183 mean?
The payer says the referring provider on the claim is not eligible to refer the service that was billed.
Is CO-183 the same as a missing referral?
No. A missing referral is usually a different code. CO-183 means a referrer was listed, but the payer won’t accept that person.
Which box holds the referring provider on the CMS-1500?
Box 17 holds qualifier DN and the name. Box 17b holds the referring provider’s NPI.
Can a chiropractor refer for an MRI?
It depends on the payer. Some plans accept chiropractors as referrers for imaging and some don’t, so check the plan’s policy.
Can I bill the patient for a CO-183 line?
No. Group code CO puts the amount on the provider, so it can’t be billed to the patient.
How is CARC 183 different from CARC 184?
CARC 183 is about the referring provider. CARC 184 is about the prescribing or ordering provider.
Sources
How we checked: each code quote on this page was matched word for word with the X12 CARC and RARC lists on 22 October 2026.
- X12, Claim Adjustment Reason Codes (CARC 183, 184, 197, 16). Accessed 22 Oct 2026.
- X12, Remittance Advice Remark Codes (N574, N575). Accessed 22 Oct 2026.
- NUCC, 1500 Claim Form instructions. Accessed 22 Oct 2026.
- CMS, Order and Referring data. Accessed 22 Oct 2026.
- CMS, NPPES NPI Registry. Accessed 22 Oct 2026.
Last updated: 22 October 2026 · Educational content; not legal advice.