Estimating True Patient Cost-Sharing Burden: Multi-Payer Claim Reconciliation in an All-Payer Claims Database.

All-payer claims databases (APCDs) comprise claims from multiple payers that can be traced to a single patient. To correctly estimate cost-sharing for an individual patient, we developed an algorithm to reconcile payments from secondary and tertiary payers to claims that are not fully covered by primary insurance. In a Colorado APCD cancer cohort (n = 70,100), reconciliation of claims across multiple payers markedly lowered estimated cost-sharing for patients with more than one source of coverage ($5,544 (no reconciliation); $5,013 (primary payer only) to $1,580). The largest reductions in cost-sharing after reconciliation were for individuals with Traditional Medicare with Medigap ($6,449→$1,123; Δ = -$5,326), dual Medicare-Medicaid ($4,439→$2,340; Δ = -$2,099), and Medicaid-commercial ($2,708→$2,009; Δ = -$699). Excluding secondary payments from estimates of cost-sharing systematically inflates cost-sharing estimates. A transparent reconciliation algorithm is necessary to correctly estimate cost-sharing and is recommended for researchers and policymakers who use the APCD for estimating costs across payers and to the patient.