CO-166: Payer's Responsibility Ended Before Service Date

What Does CO-166 Mean?

With CO (Contractual Obligation), the CARC 166 adjustment is the provider's responsibility. The payer denied or reduced payment because of the patient's insurance plan with this payer ended before the date the service was rendered, so the payer is no longer responsible for processing claims. The patient is not liable for this amount. If the denial is in error, the provider can correct and resubmit the claim or file an appeal with supporting documentation.

CARC 166 indicates payer's responsibility ended before service date. 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: the patient's insurance plan with this payer ended before the date the service was rendered, so the payer is no longer responsible for processing claims; The employer group switched insurance carriers or terminated the plan, and the service was rendered after the transition date; The payer retroactively terminated the patient's coverage, and claims for services rendered during the period that is now uncovered are being denied. The group code paired with CARC 166 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

How to Resolve

1. Review the remittance details Examine the CO-166 adjustment and any accompanying RARC codes to identify the specific reason for the denial.
2. Identify the root cause Determine which issue applies: patient's coverage with this payer terminated before date of service, employer group plan terminated or changed carriers, retroactive coverage termination, among others.
3. Correct the claim Address the identified issue — update the claim data in your billing system to resolve the payer's responsibility ended before service date problem.
4. Resubmit the corrected claim Submit the corrected claim following the payer's resubmission guidelines. Include any supporting documentation that addresses the denial reason.
5. Appeal if the original claim was correct Appeal if the patient had active coverage on the date of service. Include proof of coverage such as eligibility verification records, member ID confirmation, or enrollment documentation showing the coverage was active when the service was rendered.

Common RARC Pairings

The RARC code tells you exactly what triggered the CO-166:

How to Prevent CO-166

• Verify patient insurance eligibility and coverage dates in real-time before each visit
• Check for coverage changes at each patient encounter, especially at the beginning of each year
• Maintain updated insurance information in patient records and ask patients about coverage changes at check-in
• Submit claims promptly to reduce the risk of coverage changes between service date and claim submission
• Implement eligibility verification automation to detect coverage terminations before services are rendered

Also Filed As

The same CARC 166 may appear with different Group Codes:

Related Denial Codes