CO-243 shows up when a plan that uses gatekeepers decides the primary care provider, or the network, never approved the visit. It is common with HMO and point-of-service plans that require a referral before a specialist sees the member. Often the referral exists. It simply never reached the claim. (Primary source: X12 Claim Adjustment Reason Codes)
In brief: CARC 243 reads “Services not authorized by network/primary care providers.” Find the referral from the member’s PCP, then report it: the referring doctor in Box 17 and the referral number in Box 23 on a CMS-1500, or FL 78 and FL 63 on a UB-04. If no referral exists, ask the PCP whether a retro referral is allowed.
Part of our denial codes library. Written by Manikandan J, CPC, CRCR, who has worked referral and authorization denials for commercial and managed care plans. Published 24 October 2026. Last updated: 24 October 2026. Code wording quoted word for word from X12.
The official meaning of CO-243
| Field | Value |
|---|---|
| Code | 243 |
| Description | “Services not authorized by network/primary care providers.” |
| Start | 06/03/2012 |
| Notes | Replaces deactivated code 38 |
Source: X12 Claim Adjustment Reason Codes, checked 24 October 2026.
A referral is the PCP’s written approval for the member to see a specialist. HealthCare.gov defines it in its referral glossary entry. A network authorization is the same idea run by the plan’s medical group. CO means the provider carries the loss, so the member cannot be billed unless they signed a waiver your contract allows.
Some payers add N54: “Claim information is inconsistent with pre-certified/authorized services.” That remark points to a referral that exists but does not match the claim.
Example scenario (fictional names), part 1
CO-243 Denial Example: What Happened
Marisol Ortega bills for Bayview Heart Associates, a fictional cardiology group. A new patient with an HMO plan came in for shortness of breath, and the cardiologist billed 99204.
The 835 came back with CAS*CO*243 and nothing paid. The front desk had scanned a referral into the chart at check-in.
If the referral was in the chart, why did the plan say it was missing? Keep reading, or jump to how the CO-243 denial was resolved.
Where CO-243 comes from
- Referral not on the claim. The paper is in the chart, but Box 17 and Box 23 are blank.
- Wrong referring doctor. A specialist or urgent care doctor is listed instead of the assigned PCP.
- Expired referral. The visit date falls after the referral end date or the visit count ran out. For example, a referral for three visits does not cover a fourth.
- PCP changed. The member switched PCPs, and the old PCP’s referral no longer counts.
- No referral at all. The member self-referred to a specialist under a plan that does not allow it.
How to fix CO-243
- Pull the referral. Confirm the referral number, the PCP’s name and NPI, the date range and the number of visits approved.
- Check the member’s PCP. Compare it with the PCP the plan has on file for the date of service.
- Report it on the claim. On a CMS-1500, put qualifier DN with the PCP’s name in Box 17, the PCP’s NPI in Box 17b and the referral number in Box 23, per the NUCC 1500 instructions. On a UB-04, use FL 78 with qualifier DN and FL 63.
- Send a corrected claim. Use Box 22 frequency code 7 with the original claim number, or type of bill xx7 with FL 64 on a facility claim.
- If there was no referral. Ask the PCP’s office whether the plan accepts a retro referral. If not, write off or appeal with records showing an emergency.
Our prior authorization guide covers the related case where a plan wants approval for the service itself, not just a referral.
Example scenario (fictional names), part 2
How the CO-243 Denial Was Resolved
Marisol opened the scanned referral. It was valid for three visits from the member’s assigned PCP, but no one had keyed it into the claim, so Box 17 and Box 23 went out blank.
Fix: She sent a corrected claim with DN and the PCP’s name in Box 17, the PCP’s NPI in Box 17b, the referral number in Box 23 and frequency code 7 in Box 22.
Outcome: The visit paid. Bayview added a check-in step that keys the referral number into the visit before the doctor sees the patient.
Names and details are illustrative; no real patient data.
- Box 17 / FL 78: qualifier DN with the member’s assigned PCP added (blank before).
- Box 17b / FL 78: the PCP’s NPI 1234567893 (sample number) added.
- Box 23 / FL 63: referral number REF-55120 added.
- Box 22 / FL 4 + FL 64: frequency code 7, or type of bill 0137, with the original claim number.
- Box 21 / FL 67: R06.02 (entered as R0602) is unchanged.
CO-243 compared with similar codes
| Code | What is missing | First step |
|---|---|---|
| CO-243 | PCP or network approval | Report the referral |
| CO-197 | Precertification or authorization | Get or report the auth |
| CO-15 | Valid authorization number | Fix Box 23 |
| PR-242 | Out-of-network provider | Check network status |
FAQ
What does CO-243 mean?
The plan says the member’s PCP or network did not authorize the service, usually because no referral was reported.
Which claim fields carry a referral?
On a CMS-1500, Box 17 (qualifier DN), Box 17b and Box 23. On a UB-04, FL 78 or FL 79 with qualifier DN and FL 63.
Can I bill the patient for CO-243?
Not under group code CO, unless the member signed a valid financial waiver your contract allows.
Does a retro referral fix CO-243?
Sometimes. Many HMOs allow a PCP to issue one within a short window. Check the plan’s provider manual.
Is CO-243 the same as old code 38?
Yes, in purpose. X12 notes that CARC 243 replaced deactivated code 38.
Sources
How we checked: each code quote on this page was matched word for word with the X12 CARC and RARC lists on 24 October 2026.
- X12, Claim Adjustment Reason Codes (CARC 243). Accessed 24 Oct 2026.
- X12, Remittance Advice Remark Codes (N54). Accessed 24 Oct 2026.
- NUCC, 1500 Health Insurance Claim Form. Accessed 24 Oct 2026.
- HealthCare.gov, Referral. Accessed 24 Oct 2026.
- NUBC, National Uniform Billing Committee. Accessed 24 Oct 2026.
Last updated: 24 October 2026 · Educational content; not legal advice.
Related denial codes
- CO-183: Referring Provider Not Eligible to Refer
- PR-242: Services Not Provided by Network or Primary Care Providers
- CO-213: Self-Referral Rule Denials
- CO-210: Authorization Received Too Late
- CO-208: NPI Not Matched Fix
- CO-207: NPI Invalid Format Fix
- CO-206: NPI Missing on the Claim
- CO-198: Precertification or Authorization Exceeded