OBJECTIVETo establish a method for evaluating the activity of von Willebrand factor cleaving protease (vWF-cp) and evaluate its clinical application.

METHODSPurified von Willebrand factor polymer was isolated by gel filtration from human fresh-frozen plasma as the enzyme substrate. SDS-PAGE, Western blotting, and luminographic detection were used to evaluate vWF-cp activity of 60 healthy adults, 28 patients with cerebral infarction (CI) and 7 with thrombotic thrombocytopenic purpura (TTP).

RESULTSIn the subjects involved, the method for evaluating vWF-cp activity had intra- and inter-batch coefficient of variation(CV) of 4.81% (n=8) and 8.63% (n=6), respectively. According to this method, the plasma vWF-cp activity in the 60 healthy adults was significantly higher than that in the CI patients [(86.53-/+17.49)% vs (77.15-/+16.72)%, P<0.05]. In TTP patients before plasma replacement, the vWF-cp activity was (9.06-/+7.17)% and increased significantly to (47.00-/+6.27)% 24 h after plasma replacement, respectively, but still significantly lower than that of healthy adults (P<0.01), whereas in the convalescent stage, the activity approached the normal level [(83.18-/+8.83)%, P>0.05].

CONCLUSIONSAccording to the described method, which allows accurate vWF-cp activity measurement with good sensitivity, specificity and reproducibility, vWF-cp activity is lower in CI patients and even more so in TTP patients than that of healthy adults. Plasma replacement can effectively increase the vWF-cp activity in TTP patients.