CO-27 means the payer says the patient's coverage had ended before the date of service.
Behavioral health facilities see it on long residential stays, when a patient loses a job or ages off a parent's plan during treatment, and on retroactive terminations for unpaid premiums.
Run eligibility for each billed date, not just the admission date. If the patient elects COBRA, coverage can be reinstated back to the date it was lost, so hold the claim and rebill once it posts. If coverage truly ended, find the next payer, such as a new employer plan or a marketplace plan.
Questions
Can CO-27 be reversed?
Yes, when coverage is reinstated, for example after a COBRA election or a premium payment within the grace period.
How do I prevent CO-27?
Re-check eligibility on a schedule during long stays, not only at admission.
Read next
Educational summary, not billing advice. Official code descriptions are at x12.org. Checked October 2026.