The clinical utility of ADAMTS13 activity, antigen and autoantibody assays in thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) has been linked to a severe deficiency in ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, member 13) activity. Since the identification of ADAMTS13, and its target cleavage sequence in von Willebrand factor (VWF), several novel ADAMTS13 activity, antigen and autoantibody assays have been developed. Our aim was to evaluate the potential use of these novel assays. ADAMTS13 activity and inhibitors were measured by overnight incubation of patient plasma with pure VWF followed by multimer or collagen binding analysis. ADAMTS13 activity (Rapid peptide assay), antigen and immunoglobulin G anti-ADAMTS13 were measured by enzyme-linked immunosorbent assay. 118 samples from seven TTP patients (six adult idiopathic, one congenital) were studied longitudinally during episodes of TTP, their treatment and prophylaxis. ADAMTS13 antigen levels varied considerably between patients and sample times, but in new cases of acute TTP, rapid assays of ADAMTS13 antigen, on serial samples, maybe helpful in confirming the diagnosis. The rapid peptide ADAMTS13 activity assay showed good concordance of results with the older activity assay methods. The change in ADAMTS13 activity mirrored the autoantibody level and in 5/6 acquired TTP cases, a fall in antibody appeared to predict a rise in ADAMTS13 activity, potentially allowing modification of patient management based on autoantibody levels.