Cost-effectiveness of rapid vs. in-house vs. send-out ADAMTS13 testing for immune thrombotic thrombocytopenic purpura

• Rapid ADAMTS13 assay utilization is a cost-saving strategy in the care of patients with intermediate and high PLASMIC scores

• Cost savings with the rapid ADAMTS13 assay are greatest in the context of empiric treatment with caplacizumab

While awaiting confirmatory results, empiric therapy for patients suspected to have immune thrombotic thrombocytopenic purpura (iTTP) provides benefits and also accrues risks and costs. Rapid assays for ADAMTS13 may be able to avoid the cost and risk exposure associated with empiric treatment. We conducted the first cost-effectiveness evaluation of testing strategies with rapid versus traditional ADAMTS13 assays in patients with intermediate to high-risk PLASMIC scores, with and without caplacizumab use. We built a Markov cohort simulation with four clinical base-case analyses: 1) Intermediate-risk PLASMIC score with caplacizumab, 2) Intermediate-risk PLASMIC score without caplacizumab, 3) High-risk PLASMIC score with caplacizumab, 4) High-risk PLASMIC score without caplacizumab. Each of these evaluated three testing strategies: 1) rapid assay (<1-hour turnaround), 2) in-house FRET-based assay (24-hour turnaround), and 3) send-out FRET-based assay (72-hour turnaround). The primary outcome was the incremental net monetary benefit (iNMB) reported over a 3-day time horizon and across accepted willingness-to-pay thresholds in USD per quality-adjusted life-year (QALY). While accruing the same amount of QALYs, the rapid assay strategy saved up to $46,820 (95% CI $41,961-$52,486) per-patient-tested. No parameter variation changed the outcome. In probabilistic sensitivity analyses, the rapid assay strategy was favored in 100% (three base-cases and scenario analyses) and 99% (one base-case and scenario analysis) across 100,000 Monte Carlo iterations within each. Rapid ADAMTS13 testing for patients with intermediate- or high-risk PLASMIC scores yields significant per-patient cost savings, achieved by reducing the costs associated with unnecessary therapeutic plasma exchange and caplacizumab therapy in patients without iTTP.