Secondary Insurance Billing for ABA Services

Understanding Coordination of Benefits (COB)

When a patient has two insurance plans, the primary payer processes the claim first. The secondary payer then pays against the patient's remaining balance (deductible, coinsurance, copay) up to their own benefit limits. ABA practices must understand COB rules to bill correctly and avoid overpayment situations.

Determining Primary vs. Secondary

• Birthday rule (children): Parent whose birthday falls earlier in the calendar year = primary for the child
• COBRA: Active coverage is primary; COBRA is always secondary
• Medicaid: Always the payer of last resort — Medicaid is always secondary

Step-by-Step Secondary Billing

1. Submit the claim to primary first; receive EOB with adjudication details
2. Create a secondary (crossover) claim with billing level = Secondary
3. Attach the primary EOB as supporting documentation
4. Fill in Box 29 (Amount Paid) on CMS-1500 with the primary payment amount
5. The secondary payer adjudicates based on what remains after primary payment

Medicaid as Secondary

Medicaid crossover claims are handled differently by state. In most states:

• Primary commercial claim must be adjudicated and denied or partially paid
• Medicaid crossover submission includes the primary EOB
• Medicaid will pay up to their fee schedule minus what primary paid