Rapid ADAMTS13 activity assays for thrombotic thrombocytopenic purpura: a systematic review and meta-analysis

• Rapid ADAMTS13 assays have turnaround times within one hour and potential to avert empiric TPE and caplacizumab in patients without TTP

• The HemosIL AcuStar CLIA is highly sensitive and specific and suitable for incorporation in diagnostic and treatment algorithms for TTP

Thrombotic thrombocytopenic purpura (TTP) is a rare, potentially fatal thrombotic microangiopathy caused by severe ADAMTS13 deficiency. Prompt treatment improves survival; however, reference standard ELISA and FRETS-VWF73 ADAMTS13 activity assays have long turnaround times that necessitate empiric treatment of many patients who ultimately are found not to have TTP. Rapid assays with analytical turnaround times within one hour have recently become available. We conducted a systematic review and meta-analysis of the performance characteristics of rapid assays relative to reference standard assays for ADAMTS13 activity for patients with suspected or confirmed TTP. Nineteen studies representing three rapid ADAMTS13 assays and 4,207 patient samples were included. The HemosIL AcuStar CLIA demonstrated high sensitivity (0.98, 95% CI 0.94 - 1.00), specificity (0.99, 0.97 - 1.00), and positive (0.96, 0.90 - 0.98) and negative predictive value (0.99, 0.99 - 1.00). The Technofluor FRET and Technoscreen assays had sensitivity of 0.93 (0.86 - 0.96) and 0.98 (0.42 - 1.00), specificity of 0.98 (0.95 - 0.99) and 0.87 (0.76 - 0.94), PPV of 0.97 (0.85 - 1.00) and 0.71 (0.59 - 0.80), and NPV of 0.96 (0.93 - 0.98) and 0.99 (0.72 - 1.00), respectively. The proportion of discrepant results (relative to reference standard assays) was 0.04 (0.03 - 0.05) for HemosIL AcuStar, 0.04 (0.02 - 0.06) for Technofluor FRET, and 0.11 (0.07 - 0.16) for the Technoscreen assay. With rapid turnaround time and high sensitivity, the HemosIL AcuStar CLIA appears able to reliably avert empiric plasma exchange, corticosteroids, and caplacizumab in patients without TTP.