Evaluation of von Willebrand factor-cleaving protease activity in patients with thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy. In this study we investigated the von Willebrand factor-cleaving protease (vWF-cp) activity deficiency in patients with TTP.The plasma or serum vWF-cp activity was measured using a sensitive enzyme-linked immunosorbent assay (ELISA) by detecting the residual collagen binding activity (R-CBA) of von Willebrand factor (vWF) before and after digestion by vWF-cp. Multimers of vWF in plasma of patients with TTP were also analyzed by SDS-agarose electrophoresis. Moreover, the serum vWF-cp activities were compared between the patients with TTP and those with tumors.The coefficient of variation for intra-batch and inter-batch of the assay were 3.60% and 8.35%. The plasma and serum vWF-cp activity in healthy individuals were (78.79 +/- 9.17)% (n = 30) and (79.47 +/- 10.78)% (n = 53), respectively, while the plasma vWF-cp activity in 5 patients with TTP was markedly decreased [(21.83 +/- 19.98)%, P < 0.001]. The unusually large vWF multimers were observed in two plasma samples of the patients with TTP. Although the vWF-cp activities in patients with benign and malignant tumors were also decreased (P < 0.03 and P < 0.001, respectively), they were relatively high in comparison with that of TTP patients (P < 0.001).Measurement of the vWF-cp activity using R-CBA is a simple and rapid method for diagnosing TTP. The vWF-cp activity in patients with TTP was markedly lower than those of patients with tumors.