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CO-P4 Denial Code: Workers' Comp Claim Non-Compensable

CO-P4 means the workers' compensation claim itself was adjudicated as non-compensable, so the carrier isn't liable for this claim or treatment. The injured worker's claim was denied under workers' comp rules, and the bill must go to other coverage unless the decision is overturned.

Quick facts

Code
CO-P4 (CARC P4)
Status
Active In use since November 1, 2013; last modified July 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The usual group. The carrier won't pay; pursue other coverage and follow state rules before billing the patient.
  • OA (Other Adjustment): Sometimes used to show responsibility shifts to another payer.
  • PR (Patient Responsibility): Used when the carrier indicates the patient is responsible. The health plan is typically billed first.
Official description
Workers' Compensation claim adjudicated as non-compensable. This Payer not liable for claim or service/treatment. Usage: If adjustment is at the Claim Level, the payer must send and the provider should refer to the 835 Insurance Policy Number Segment (Loop 2100 Other Claim Related Information REF qualifier 'IG') for the jurisdictional regulation. If adjustment is at the Line Level, the payer must send and the provider should refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment information REF). To be used for Workers' Compensation only
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-P4 means

CARC P4 says workers’ compensation claim adjudicated as non-compensable. This payer not liable for claim or service/treatment. X12 limits it to workers’ compensation. It replaced deactivated CARC 214. As with other jurisdictional P codes, the carrier must cite the regulation in the 835: loop 2100 REF qualifier IG for claim-level adjustments, and loop 2110 REF for line-level ones.

“Non-compensable” is broader than “not work-related.” A workers’ comp claim can be denied because the injury wasn’t reported on time, the worker wasn’t a covered employee, the employer raised a legal defense, or the condition isn’t covered under state law. In all of these, the carrier has decided the whole claim doesn’t qualify, so every bill tied to it is denied.

Common causes

  • Claim denied by the carrier after investigation.
  • Late reporting of the injury under state rules.
  • Worker not covered, for example an independent contractor.
  • Condition excluded by state workers’ comp law.
  • Claim withdrawn by the worker (N624).

How to fix it

  1. Get the carrier’s written denial and the regulation cited.
  2. Ask the patient whether they’re disputing the decision with the state workers’ comp agency.
  3. Bill the health plan or other coverage, attaching the denial and correcting box 10a.
  4. Track the dispute. If the claim is later accepted, rebill the carrier and reconcile payments from other payers.
  5. Follow state rules before billing the injured worker.

How to prevent problems

  • Verify the workers’ comp claim status with the carrier before treatment and periodically during care.
  • Keep health insurance on file for every workers’ comp patient.
  • Record the claim number, adjuster, and date of injury on the account so status checks are quick.

Specialty notes

Occupational medicine and orthopedic practices often begin treatment before compensability is decided. A clear intake process for pending claims helps avoid long stretches of unbilled care when a claim is denied.

Remark codes that may appear with CO-P4

  • N607 (Service provided for non-compensable condition(s).): Service provided for non-compensable conditions.
  • N436 (The injury claim has not been accepted and a mandatory medical reimbursement has been made.): The injury claim hasn't been accepted, and a mandatory medical reimbursement was made.
  • N624 (The associated Workers' Compensation claim has been withdrawn.): The associated workers' comp claim was withdrawn.
  • CO-214Deactivated (Workers' Compensation claim adjudicated as non-compensable.): The deactivated code that CARC P4 replaced.
  • CO-P2 (Not a work related injury/illness and thus not the liability of the workers' compensation carrier): Specifically not work-related, a narrower reason than non-compensable.
  • OA-19 (This is a work-related injury/illness and thus the liability of the Worker's Compensation Carrier.): A health plan says the injury belongs with workers' comp.
  • CO-P8 (Claim is under investigation.): The claim is still under investigation, before a compensability decision.

CO-P4 FAQ

How is CO-P4 different from CO-P2?

CO-P2 says the injury isn't work-related. CO-P4 says the workers' comp claim was ruled non-compensable, which can be for many reasons, such as late reporting, the worker's status, or a legal defense, even if the injury happened at work.

Where do I bill after CO-P4?

Usually the patient's health plan, with the carrier's non-compensability determination attached so the plan doesn't deny it as work-related.

What if the worker appeals and wins?

If the claim is later found compensable, rebill the carrier. You may need to refund the health plan for services it paid.

Can I bill the injured worker?

Only after other coverage is exhausted and state rules allow it. Some states protect workers from bills while a compensability dispute is pending.

Is CO-P4 used by health plans?

No. X12 limits it to workers' compensation claims.

Does CO-P4 apply to every bill on the claim?

Usually yes. A non-compensability decision applies to the whole workers' comp claim, so all related bills from every provider are typically denied until the decision changes.