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CO-165 Denial Code (Deactivated): Referral Absent/Exceeded

CO-165 meant a required referral was missing, or the services went beyond what the referral allowed. X12 deactivated it without naming a successor; CARC 288 now covers a missing referral and CARC 287 an exceeded one.

X12 deactivated CARC165 on May 1, 2018. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-165 (CARC 165)
Status: Deactivated StoppedMay 1, 2018 (in use since October 31, 2004).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): Securing the referral was treated as the provider's responsibility, so the amount was not billed to the patient.
Official description: Referral absent or exceeded.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-165 meant

Many HMO and managed care plans require a referral from the member’s primary care provider before a specialist visit is covered. CARC 165 told the specialist that either there was no referral on file for the visit or the visit fell outside what the referral covered, for instance after its visit count or end date.

What replaced it

X12 did not name a replacement, but the two parts of the old code became separate active codes:

CO-288 for an absent referral.
CO-287 for a referral that was exceeded.

When the issue is framed as a lack of PCP or network authorization, some payers use CO-243.

If you still see CO-165

It will mostly surface in older denials. Check the payer portal for referrals linked to the patient and your NPI, and compare their dates and visit counts to the claim. If a valid referral exists, add its number and resubmit. If not, ask the primary care office whether a retroactive or extended referral is possible. Visits that cannot be covered by a referral are generally written off under your contract.

CO-288 (Referral absent): Referral absent.
CO-287 (Referral exceeded): Referral exceeded.
CO-243 (Services not authorized by network/primary care providers.): Services not authorized by network or primary care providers.

CO-165 FAQ

What does an exceeded referral look like?

The referral existed but the patient was seen more times, or for longer, than it allowed, or for services it did not include. Visits past the limit are denied until a new or extended referral is issued.

Can a referral be obtained after the visit?

Some plans allow a retroactive referral from the primary care provider within a short window. Check the plan's rules and request one promptly.

Important: read before using this information

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