CO-111: Not Covered Unless Provider Accepts Assignment

What Does CO-111 Mean?

CO-111 means the provider must write off the denied amount because assignment was not accepted for a service that requires it. This typically happens when the assignment indicator was not checked on the claim form or the provider's participation status does not match the payer's requirements. The patient cannot be billed for this provider-side error.

CARC 111 fires when a payer denies a claim because the provider did not accept assignment for a service that requires it. Assignment means the provider agrees to accept the payer's approved fee schedule amount as payment in full and will not balance bill the patient beyond the allowed coinsurance, copay, or deductible. Certain services — particularly under Medicare — require mandatory assignment regardless of the provider's general participation status.

The most common trigger is Medicare mandatory assignment services. Clinical laboratory services, ambulance services, drugs and biologicals administered by physicians, and services to dual-eligible (Medicare/Medicaid) patients all require assignment under Medicare rules. If the claim does not indicate assignment acceptance, Medicare will deny it with CARC 111 even if the provider is a participating provider. The second major trigger is simply a missing assignment indicator — Box 27 on the CMS-1500 form or the electronic equivalent was not checked, causing the payer to process the claim as non-assigned.

The resolution depends on the Group Code. CO-111 means the provider must absorb the denied amount and correct the claim. PR-111 shifts the financial burden to the patient, typically when the provider is non-participating and the service does not require mandatory assignment. In PR scenarios, the patient pays the full charge because the provider did not agree to accept the payer's allowed amount.

Common Causes

How to Resolve

Verify the provider's participation status and assignment indicator on the claim, correct any errors, and resubmit with assignment accepted if the service requires it.

1. Review the assignment indicator Check whether Box 27 on CMS-1500 (or the electronic equivalent) was properly completed. A missing or unchecked assignment box is the most common cause.
2. Verify participation status Confirm the provider is enrolled and participating with the payer. If enrollment lapsed, initiate re-enrollment and ask about retroactive effective dates.
3. Identify mandatory assignment requirements Determine if the service requires mandatory assignment under Medicare or the specific payer's rules — clinical lab, ambulance, physician-administered drugs, and dual-eligible services all require assignment.
4. Correct and resubmit Add or correct the assignment acceptance indicator and resubmit the claim. For mandatory assignment services, ensure assignment is always indicated regardless of general participation status.

Common RARC Pairings

The RARC code tells you exactly what triggered the CO-111:

How to Prevent CO-111

• Ensure all claims have the assignment acceptance indicator properly completed before submission, especially for Medicare mandatory assignment services
• Maintain current provider enrollment and participation status with all active payers, with renewal reminders set before expiration
• Build claim scrubbing rules that flag claims missing the assignment indicator before submission
• Train billing staff on which services require mandatory assignment under Medicare (lab, ambulance, drugs, dual-eligible)
• Regularly audit provider enrollment records to verify participation status matches billing practices
• Implement default assignment acceptance in billing templates for mandatory assignment service types

General Prevention

• Maintain current provider enrollment and participation status with all active payers, and set up renewal reminders before enrollment lapses
• Ensure all claims have the assignment acceptance indicator properly completed before submission, particularly for Medicare mandatory assignment services
• Train billing staff on which services require mandatory assignment under Medicare and other payers
• Implement claim scrubbing rules that flag claims missing the assignment indicator before submission
• Stay informed about payer policy changes regarding assignment requirements

Also Filed As

The same CARC 111 may appear with different Group Codes:

Related Denial Codes