What Does CO-27 Mean?

CO-27 indicates that the payer believes the patient’s coverage ended before the date the service was provided. CARC 27 is defined as expenses incurred after coverage terminated. When it appears with the CO group code, the payer is assigning the adjustment as a contractual obligation, which means the billing team should not automatically move the denied amount to the patient without first confirming the payer contract, eligibility facts, and applicable billing rules. This denial is primarily an eligibility-timing issue. The key question is whether the payer’s termination date is correct for the date of service. Coverage may truly have ended because of an employment change, premium issue, plan change, COBRA expiration, Medicaid eligibility loss, or another event. In other cases, coverage may have been reinstated, retroactively updated, or replaced by another plan. The correct resolution depends on verifying the coverage history, identifying the responsible payer for the service date, and preserving evidence of any eligibility verification completed before care was delivered.

Common Causes of CO-27

• Coverage terminated before the date of service: The member’s policy ended because of employment termination, a plan change, loss of eligibility, premium nonpayment, COBRA expiration, or another coverage-ending event.
• Eligibility was checked too early or not reverified: The practice may have verified coverage at registration or an earlier visit but did not confirm eligibility again near the date of service. A termination occurring between those dates can therefore be missed.
• The patient has new or replacement insurance: The old plan may correctly deny because another payer became responsible. If the patient’s new insurance was not captured, the claim can be sent to a payer whose coverage had already ended.
• Coverage was retroactively terminated or later reinstated: Payers sometimes adjust eligibility after the service date. A claim may deny based on a retroactive termination even though the provider previously received an active eligibility response, or a denial may remain after coverage is later reinstated.

How to Identify the Exact Reason for CO-27

• Verify effective and termination dates for the exact service date: Check the payer portal, 271 eligibility response, or payer representative for the member’s coverage span. Do not rely only on the current status because the question is whether coverage was active on the historical date of service.
• Review the patient’s insurance history: Ask about employer changes, new plans, COBRA, Medicaid/Medicare changes, marketplace coverage, or secondary insurance. Compare those details with insurance cards and the registration record.
• Check prior eligibility evidence and authorization records: If the practice verified active coverage or obtained authorization before the service, preserve the transaction response, portal screenshot, reference number, and timestamp. This can support payer reprocessing or an appeal.
• Confirm whether another payer is responsible: Run eligibility for any replacement plan and review coordination-of-benefits order. If another payer was active, determine whether the claim can still be submitted within timely-filing rules and what proof of the original denial is required.

How to Resolve or Appeal CO-27

• Bill the correct active payer when replacement coverage exists: Update the insurance record and submit the claim to the plan that was active on the date of service. Include the prior payer denial when the new payer requires proof for timely-filing consideration.
• Request reprocessing when coverage was actually active: If the payer’s termination date is incorrect or coverage was reinstated, provide the eligibility evidence and ask the payer to update the member record and reprocess the claim.
• Appeal retroactive termination when supported: When coverage was verified as active before service but later retroactively terminated, follow the payer’s appeal process and include the dated eligibility response, authorization record, payer references, and any applicable plan or regulatory documentation.
• Handle any remaining patient balance cautiously: If no insurance was active, follow the organization’s financial policy and applicable notice, contract, and billing requirements. A CO adjustment should not be shifted to the patient merely because the payer did not pay; first confirm whether patient billing is permitted.

How to Prevent CO-27 Denials

• Verify eligibility close to every date of service: Recheck coverage for scheduled services, recurring therapy, procedures, and high-value care even when the patient has been seen before. Eligibility can change without an obvious change in the patient record.
• Capture coverage changes during scheduling and check-in: Prompt staff to ask about employer changes, new insurance cards, COBRA, Medicaid renewals, and plan-year changes. Update payer and member information before the claim is generated.
• Retain proof of eligibility transactions: Store the 271 response, portal confirmation, verification date/time, and payer reference with the account. Evidence is especially valuable when a payer later applies a retroactive termination.
• Monitor long treatment episodes for coverage changes: For therapy, oncology, behavioral health, home health, and other recurring services, schedule periodic eligibility rechecks instead of relying on the verification performed at the start of care.