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CO-W5 Denial Code (Deactivated): Not Authorized for WC

CO-W5 meant the medical provider was not authorized or certified to treat injured workers in that jurisdiction. X12 deactivated it and its notes direct payers to code P16.

X12 deactivated CARCW5 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.

Code: CO-W5 (CARC W5)
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 bore the denial because its workers' compensation authorization was lacking.
OA (Other Adjustment): The code's text also allowed the OA group, used when the payer did not assign the amount to the provider as a contractual matter.
Official description: Medical provider not authorized/certified to provide treatment to injured workers in this jurisdiction. (Use with Group Code CO or OA)
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-W5 meant

CARC W5 was a workers’ compensation enrollment denial. Certain jurisdictions only pay providers that are authorized or certified to treat injured workers, sometimes through a network. If the treating provider did not meet that requirement, the claim was denied with this code.

What replaced it

X12’s note says to use code P16. CO-P16 now carries the same description in the P-series. Where a medical provider network drives the adjustment, carriers use CO-P25. On health plan claims, the comparable concept is CO-185.

If you still see CO-W5

Only older workers’ compensation files should have it. If a similar denial appears now, check the state’s requirements for treating injured workers and whether your provider is registered, certified, or in the employer’s network. Complete the enrollment if possible, and ask whether the state allows retroactive approval or a transfer of care.

CO-P16 (Medical provider not authorized/certified to provide treatment to injured workers in this jurisdiction.): Named replacement: medical provider not authorized or certified to treat injured workers in this jurisdiction.
CO-P25 (Payment adjusted based on Medical Provider Network (MPN).): Payment adjusted based on a Medical Provider Network.
CO-185 (The rendering provider is not eligible to perform the service billed.): The health plan equivalent when the rendering provider is not eligible.

CO-W5 FAQ

Why would a provider need workers' comp authorization?

Some states require providers to register, be certified, or belong to an approved network before treating injured workers under workers' compensation.

Can the injured worker be billed?

Generally not without checking state law. Workers' compensation rules often restrict billing the worker, even when the provider was not authorized.

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