Evidence that von Willebrand factor is not required for the clotting of plasma in the presence of platelets and kaolin (Hardisty-Hutton test).

Antihemophilic factor (AHF) essentially free of von Willebrand factor (vWF) was used to determine whether vWF affected the coagulant activity of AHF in a kaolin-activated system using platelet-rich plasma. The AHF was prepared by sequential chromatography on solid-phase polyelectrolyte (PE E-5), and on Sepharose CL-4B in the presence of a high concentration of CaCl2. Residual traces of vWF antigen were removed by affinity chromatography with immobilized anti-vWF IgG. The essentially vWF-free AHF corrected the clotting defect of plasma from three patients with severe von Willebrand's disease (vWD) as measured by the kaolin-activated clotting time in the presence of normal or vWD platelets ( Hardisty - Hutton test). Addition of hemophilic plasma as a source of vWF did not cause additional improvement, nor did a potent antibody to vWF raised in rabbits inhibit the ability of AHF to shorten the clotting time of vWD plasma. Thus we found no evidence that vWF is necessary for AHF to function in the coagulation of recalcified kaolin-activated vWF-deficient platelet-rich plasma.