CO-21
CARC
CO-21: This injury/illness is the liability of the no-fault carrier.
The official meaning of claim adjustment reason code CO-21 is below. We have not written a plain-English translation for this code yet; the search box on the translator covers the codes practices see most often.
CO = Contractual Obligation. The provider owes the difference. The patient cannot be billed for this amount. The same reason code can appear with a different group code; the group decides who may be billed.
How to use this code
Read the remark code (N, M or MA) printed with this reason code; it usually names the exact field or policy. If the claim had an error, fix it and send a corrected claim inside the timely filing limit. If the claim was right, appeal with records inside the payer's appeal window.