Coordination of Benefits (COB)

Coordination of benefits is the rules deciding which plan pays first when a patient has more than one; a stale or wrong COB order (CARC 22, OA) is a common denial that's usually a sequencing fix, not a coverage problem.

Coordination of benefits (COB) is the set of rules that decides the payment order when a patient is covered by more than one plan — which is primary, which is secondary, and how the secondary picks up what the primary didn't. When the COB order is unclear, out of date, or the primary payer's EOB wasn't attached to the secondary claim, the payer holds or denies the claim, typically as CARC 22 ('this care may be covered by another payer per coordination of benefits'), usually carrying an OA group code. The important insight is that COB denials are almost always a sequencing problem, not a coverage problem: the money is there, it's just waiting for the order to be resolved. Once you confirm which plan is primary, get the primary's EOB, and submit the secondary claim correctly, the claim pays. COB issues also drive timely-filing problems, because a claim that bounces between primary and secondary can age out — but the secondary's clock often runs from the primary's remit date, which resets the deadline in your favor. Keeping the patient's COB record current at check-in prevents most of these, but for the ones that slip through, the fix is administrative, not an argument about whether the service was covered.

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