Key Points
- When a client carries two plans, the order of payment is set by rule between the insurers - it is not a choice the family or the practice gets to make.
- A secondary claim generally cannot go out until the primary has finished adjudicating, so a slow first payer eats into the second one's filing window.
- Stale coverage records are a routine denial cause, and the fix usually belongs to the family, since payers accept the update only from the member.
Coordination of Benefits (COB) Explained
Dual coverage is common enough in ABA that most practices meet it early: a child covered by both parents' employer plans, a commercial plan alongside Medicaid, or coverage that changes mid-treatment when a parent changes jobs. Coordination of benefits is the machinery that keeps two insurers from each paying as though they were the only one, and it exists to make sure the combined payment does not exceed the cost of the care.
Which plan pays first is decided by rule rather than preference. A plan covering someone as an employee generally pays before a plan covering them as a dependent. For a child covered by both parents, many plans apply the birthday rule, where the parent whose birthday falls earlier in the calendar year holds the primary plan. Custody arrangements and court orders override the default, and Medicaid is treated as the payer of last resort behind any other coverage.
Mechanically, the practice bills the primary plan, waits for it to adjudicate, and then submits to the secondary with the primary's payment detail attached. The secondary considers the claim against its own allowed amount and pays some portion of what is left, which is frequently less than the family expects - a second plan reduces the balance rather than guaranteeing it disappears.
The sequencing has a deadline cost that catches practices out. The secondary claim cannot be finished until the primary remittance arrives, and depending on the contract the secondary's timely filing clock may have been running from the date of service the entire time. A primary payer that takes months to adjudicate can leave a narrow window on a claim nobody was late to work.
Most COB denials are records problems rather than payment disputes. A payer that believes other coverage exists will hold claims until its file is corrected, and it will generally accept that correction only from the member - so the practice's role is to notice the pattern, tell the family precisely which insurer to call, and follow up, rather than to appeal a decision that is not really about this claim.
The defense is doing the work at intake and repeating it. Ask about all coverage rather than the card the family produces first, record which plan is primary and why, re-verify at plan renewal and after any job change, and keep the primary remittance attached to the secondary claim. Long courses of treatment cross plan years, and coverage that was accurate at intake is one of the quieter ways a clean claim goes bad.