Evaluation of assay methods to measure plasma ADAMTS13 activity in thrombotic microangiopathies.

The mechanistic observations on the role of von Willebrand factor (VWF), ADAMTS13 and their interactions in the pathophysiology of thrombotic microangiopathies (TMAs), and in particular of thrombotic thrombocytopenic purpura (TTP), have recently yielded a proliferation of assays for the measurement of ADAMTS13 activity. These assays are generally based upon the cleavage by plasma ADAMTS13 of full-length VWF or synthetic VWF peptides (A2 domain, 73aa- or 78aa- fragment), followed by the direct or indirect detection of VWF cleavage products (1). The assays based on full-length VWF are sensitive (3 6% of ADAMTS13 activity) and quite reproducible but timeconsuming (2 3 days) and performed in non-physiological conditions that require the use of denaturing agents to promote the susceptibility of full-length VWF to cleavage. On the other hand, the assays based on VWF peptides are very sensitive (1 3% of ADAMTS13 activity), reproducible, easy, rapid (1 4 hours), and performed in the absence of denaturing agents, but they use non-physiologic substrates.