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CO-W6 Denial Code (Deactivated): WC Referral Not Authorized

CO-W6 meant the referral was not authorized by the attending physician as required by regulation. X12 deactivated it and its notes direct payers to code P17.

X12 deactivated CARCW6 on July 1, 2014. 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-W6 (CARC W6)
Status
Deactivated StoppedJuly 1, 2014 (in use since June 2, 2013).
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The provider who received the unauthorized referral bore the denial.
Official description
Referral not authorized by attending physician per regulatory requirement.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-W6 meant

In many workers’ compensation systems, the injured worker’s attending physician controls referrals to specialists, therapists, and other providers. CARC W6 denied care that was delivered on a referral the attending physician had not authorized as the regulations required.

What replaced it

X12’s note says to use code P17. CO-P17 now reports a referral not authorized by the attending physician per regulatory requirement. Related workers’ compensation codes include CO-P16 for provider authorization. On health plan claims, a missing referral is CO-288.

If you still see CO-W6

Expect it only in older workers’ compensation files. For a current case, confirm who the attending physician of record is and obtain a written referral that meets the state’s requirements. Keep a copy in the chart and send it with the bill. Checking referral status at intake for injured-worker patients avoids most of these denials.

  • CO-P17 (Referral not authorized by attending physician per regulatory requirement.): Named replacement: referral not authorized by attending physician per regulatory requirement.
  • CO-P16 (Medical provider not authorized/certified to provide treatment to injured workers in this jurisdiction.): Provider not authorized or certified to treat injured workers in the jurisdiction.
  • CO-288 (Referral absent): The health plan equivalent when a referral is absent.

CO-W6 FAQ

Who is the attending physician in a workers' comp case?

Usually the treating physician who manages the worker's care for the injury. Many states route specialist or ancillary care through that physician's referral.

How is this fixed?

Ask the attending physician to issue the referral in the form the state or carrier requires, then resubmit, if the rules allow a referral after the service.