Retrospective studies of patients with
thrombotic microangiopathies (TMAs) have shown that a deficient activity of
von Willebrand factor (
vWF)-cleaving protease is involved in
thrombotic thrombocytopenic purpura (
TTP) but not in the
hemolytic-uremic syndrome (HUS). To further analyze the relevance of this enzymatic activity in TMA diagnosis, a 20-month multicenter study of
vWF-cleaving protease activity was conducted in adult patients prospectively enrolled in the acute phase of TMA. Patients with sporadic (n = 85), intermittent (n = 21), or familial recurrent (n = 5) forms of TMA (66 manifesting as
TTP and 45 as HUS) were included. TMA was either idiopathic (n = 42) or secondary to an identified clinical context (n = 69).
vWF-cleaving protease activity was normal in 46 cases (7
TTP and 39 HUS) and decreased in 65 cases (59
TTP and 6 HUS). A
protease inhibitor was detected in 31 cases and was observed only in patients manifesting
TTP with a total absence of
protease activity. Among the 111 patients, mean vWF
antigen levels were increased and the multimeric distribution of vWF was very heterogeneous, showing either a defect of the high-molecular-weight forms (n = 40), a normal pattern (n = 21), or the presence of unusually large multimers (n = 50). Statistical analysis showed that vWF-
protease deficiency was associated with the severity of
thrombocytopenia (P <.01). This study emphasizes that
vWF-cleaving protease deficiency specifically concerns a subgroup of TMA corresponding to the
TTP entity.