Evaluation and clinical application of a new method for detecting ADAMTS13 activity

Background A severe deficiency of ADAMTS13 activity contributes to the pathogenesis of thromboticthrombocytopenic purpura (TTP). Measuring the activity of ADAMTS13 is helpful for the diagnosis of TTP and theprognostic monitor in TTP patients. Most available assays are cumbersome and costly, so not easily adapted to routinelaboratories. ADAMTS13 cleaves von Willebrand factor (VWF) within the domain A2, located between domains A1 andA3. Therefore, specific assays for ADAMTS13 activity could be based on the different structures of VWF before and afterthe cleavage. Using this hypothesis we try to establish a new and simple method to determine ADAMTS13 activity.Methods First, plasma samples were exposed in denaturing condition to allow cleavage of VWF by ADAMTS13. Then,the ADAMTS13 activity was measured with two novel monoclonal antibodies, SZ-129 and SZ-125, which specificallyrecognize the VWF A1 and A3 domains by using a two-site sandwich ELISA. Compared with a residual-collagen bindingassay (R-CBA), plasma ADAMTS13 activities in 161 samples were assessed, and the inhibitory activities of ADAMTS13autoantibody in 24 TTP patients were determined. The relationship of these two assays was analyzed by linearcorrelation, and the sensitivity and specificity of the new assay was also evaluated.Results Plasma ADAMTS13 activities in normal people and TTP, acute myocardial infarction (AMI), and idiopathicthrombocytopenic purpura (ITP) patients determined by the new assay were (89.75±7.93)%, (17.63±18.71)%,(68.55±18.08)%, (85.83±9.84)%, respectively. Results were consistent with those of R-CBA, the squared correlationfactor was 0.9183 of the two assays. The new assay can easily discriminate a TTP plasma sample from a non-TTPplasma sample (P<0.01), and the coefficient of variation for the new assay was 6.17%. In 23 idiopathic TTP patients, theinhibitor activity of ADAMTS13 autoantibody ranged from 12% to 100%, while no inhibitory activity was detected in onehereditary TTP patient.Conclusion This new and simple assay for ADAMTS13 activity could be used routinely in the clinic to determine theactivity of ADAMTS13.