CARC 21: This injury/illness is the liability of the no-fault carrier.

CARC 21 appears on the 835 ERA (Electronic Remittance Advice) that the payer returns after claim adjudication. It explains a reduction, denial, or payment adjustment to your billing team. For your practice, the question is workflow: identify the pattern, route the denial to the right resolution path (rebill, appeal, write-off), and recover what's recoverable without burning RVU time on dead-end fights.

What CARC 21 means

The official X12 description is: “This injury/illness is the liability of the no-fault carrier.”

In plain language: This injury/illness is the liability of the no-fault carrier.

Practice workflow for CARC X 21

Appeal with documentation specific to this code. The provider's billing office can help clarify what the carrier wants.

ApprovalHelp auto-drafts the appeal letter against the right federal appeal-rights regulation (ACA §2719, ERISA §503, NSA §2799A, 42 CFR 422 Subpart M, or 42 CFR 438 Subpart F) for the patient's plan type, the payer's own coverage policy, and the relevant clinical guideline. Drafts route to the clinician for signature in under five minutes.

CARC 21 group codes explained

On the 835 ERA, CARC 21 appears alongside a group code that signals who is financially responsible for the adjustment. CO (Contractual Obligation) — Contractual write-off. The provider agreed to the rate. Patient does NOT owe this amount.