Build and submit a secondary claim with primary EOB data populated in the correct X12 837 loops for crossover billing

Steps

1. Obtain the primary payer's EOB (paper or electronic 835 ERA): record the paid amount, contractual adjustment, patient responsibility, payment date, and the primary payer's own claim control number for each service line
2. In the secondary 837 claim, populate SBR segment in Loop 2000B: SBR01 payer responsibility sequence code '2' (secondary) or '3' (tertiary), SBR09 claim filing indicator code for the secondary payer type (e.g., 'CI' commercial, 'MB' Medicare Part B, 'MC' Medicaid)
3. Add Loop 2320 (other subscriber information) for the primary payer: OI03='Y' (benefits assigned), SBR01='P' (primary) in the nested NM1*PR name loop; include COB claim-level AMT segments: AMT*D (primary paid), AMT*EAF (remaining patient liability)
4. At each service line, add Loop 2430 (line adjudication information): SVD01 (primary payer ID), SVD02 (primary paid amount per line), SVD03 (procedure code composite matching the SV1), SVD05 (units); then CAS segments for each primary adjustment group/reason code/amount
5. Include DTP*573 (claim adjudication date) in both Loop 2320 and Loop 2430 to document when the primary adjudicated; many secondary payers reject COB claims missing adjudication date
6. Submit to the secondary payer; verify the secondary 835 ERA credits the COB correctly by confirming the paid amount plus primary paid equals or approaches the billed amount less contractual adjustments