Platelet von Willebrand factor assay: results using two methods for platelet lysis.

Two different methods (using Triton X-100 and glycerol) for lysing platelets to measure platelet vWF concentrations were compared directly. The platelet concentration of von Willebrand factor antigen (vWF:Ag) was similar for both methods, whereas ristocetin cofactor activity (Ricof) was higher with Triton than with glycerol. After storing platelet lysates for two months at -80 degrees C vWF:Ag and Ricof concentrations decreased with both methods of lysis. Larger than normal (supranormal) vWF multimeric forms could be visualized in platelet lysates obtained using both methods, with no change of the multimeric pattern during storage. Triton can be recommended as the agent of choice to lyse platelets for measurement of their vWF concentration, but the samples must be assayed within two weeks to avoid decay of Ricof activity.