CARC 21 Active

CO-21: No-Fault Carrier Responsible

TL;DR

Provider responsibility — correct and resubmit to the appropriate payer. The patient is not liable for this amount.

Action
Resubmit
Who Pays
Provider
Appeal
Yes
Patient Impact
None
Disclaimer
This content is for informational purposes only and does not constitute professional billing advice. Always verify information against your payer contracts and current coding guidelines. Consult a certified billing specialist for specific claim issues.

What Does CO-21 Mean?

With CO (Contractual Obligation), the CARC 21 adjustment for no-fault carrier responsible indicates the claim needs to be corrected or routed to a different payer. The patient is not liable for this amount. Correct the issue and resubmit.

CARC 21 indicates no-fault carrier responsible. The payer determined that the service or a portion of it does not meet coverage criteria under the patient's current plan benefits or the applicable coverage rules.

Common scenarios that trigger this adjustment include: injury from auto accident in a no-fault insurance state billed to health plan instead of PIP/no-fault carrier; Personal Injury Protection (PIP) benefits have not been exhausted, and the no-fault carrier should pay first; Health plan's system flagged the claim as no-fault based on diagnosis or condition codes. The group code paired with CARC 21 determines who bears the financial responsibility — CO places it on the provider as a contractual obligation, OA indicates a coordination of benefits or other payer adjustment, PR shifts it to the patient.

Common Causes

Cause Frequency
Auto accident in no-fault state Injury from auto accident in a no-fault insurance state billed to health plan instead of PIP/no-fault carrier Most Common
PIP benefits not exhausted Personal Injury Protection (PIP) benefits have not been exhausted, and the no-fault carrier should pay first Common
Payer identified no-fault condition Health plan's system flagged the claim as no-fault based on diagnosis or condition codes Common

How to Resolve

  1. Review the denial reason Examine the CO-21 adjustment and any RARC codes to identify what needs to be corrected.
  2. Correct the claim Address the issue that triggered the denial — update the claim with correct information or route to the appropriate payer.
  3. Resubmit the claim Submit the corrected claim per the payer's guidelines.
Appeal Guide

If PIP/no-fault benefits are exhausted, appeal with the no-fault carrier's exhaustion letter or EOB. If the injury is not auto-related, appeal with documentation showing no auto accident involvement.

Common RARC Pairings

The RARC code tells you exactly what triggered the CO-21:

RARC Description
N36 Claim must meet primary payer requirements Submit to no-fault carrier first →
N479 Missing/incomplete/invalid condition information Provide accident details and PIP status →

How to Prevent CO-21

Also Filed As

The same CARC 21 may appear with different Group Codes:

OA-21 PR-21

Related Denial Codes

CO-19 — Workers' Compensation Claim CO-20 — Liability Carrier Responsible CO-22 — Coordination of Benefits - Another Payer May Cover CO-276 — Prior Payer Denied Services Not Covered by This Payer CO-226 — Provider Information Not Provided or Insufficient

Sources

  1. https://x12.org/codes/claim-adjustment-reason-codes
  2. https://revenuecyclemgmt.com/claim-adjustment-reason-codes/
  3. https://www.rivethealth.com/blog/carcs-rarcs-claim-adjustment-remittance-advice-codes
  4. Codes maintained by X12. Visit x12.org for official definitions.