Multicentric evaluation of the new HemosIL Acustar^® chemiluminescence ADAMTS13 activity assay

Thrombotic thrombocytopenic purpura (TTP) is a rare life-threatening thrombotic microangiopathy (TMA) characterized by the severe deficiency of ADAMTS13 activity (<10%). Rapid ADAMTS13 testing is crucial for early diagnosis and optimal management of TTP patients and other TMAs. The objective of this study was to retrospectively evaluate the performance of the recently commercialized HemosIL Acustar^® ADAMTS13 activity chemiluminescent immunoassay (Instrumentation Laboratory, Bedford, Massachusetts, United States) in a multicentric study between Spain and Portugal.

A comparison method was performed to compare HemosIL Acustar^® with an in-house FRETS-VWF73 assay and two commercial ELISA assays: the TECHNOZYM^® ADAMTS13 Activity (Technoclone GmbH, Vienna, Austria) and the DG-EIA ADAMTS-13 Activity (Diagnostic Grifols, SA, Barcelona, Spain). A set of 241 frozen plasma samples with known ADAMST13 levels was used. Agreement between methods was assessed with focus on two cut-off ADAMTS13 activity values: <10% (the clinical accepted cut-off value to confirm TTP diagnosis) and <5%.

HemosIL AcuStar^® showed high agreement with the other methods in correctly classify patients with ADAMTS13 values below 10% (Kappa = 0.89) and even below 5% (Kappa = 0.94) with no false negatives and few false positives (5.40%; 95% CI: 2.20 to 8.60%). However, it also tended to underestimate ADAMTS13 levels, especially for the high assay range values (>40%) (absolute mean bias of 8.40% (95% CI: 6.53 to 10.42%)) when compared to other assays.

HemosIL AcuStar^® is highly sensitive to detect ADAMTS13 values below 10% and 5%. A large prospective validation study is needed to corroborate its utility in clinical practice.