The relationship between vWF protease activity to the platelet counts and vWF antigen levels.

The greatest reduction of vWF protease activity (1+) was evident in samples from patients with a variety of thrombocytopenic disorders, including 6 patients with TTP, 2 patients with SLE, 1 patient with ITP, and 3 patients with DIC. This group of patients also had lower platelet counts (P < .001) (A) and higher vWF antigen levels (P < .001) (B). Statistical analysis was done using a nonpaired Student t test (Minitab).