Platelet von Willebrand factor: comparison with plasma von Willebrand factor.

Platelet von Willebrand factor (vWf) was compared to its plasma counterpart. The platelet vWf was different from plasma vWf in that the multimeric organization was different, larger multimers were present, and the ratio of vWf activity to antigen was higher. Platelet and plasma vWf were similar in their antigenic reactivity in the electroimmunoassay and by liquid phase radioimmunoassay. The amount of vWf activity in large platelets was significantly higher than in normal platelets while the antigen content, although somewhat higher, was not significant. These studies show differences between normal platelet and plasma vWf, and also suggest that platelet size must be considered when platelet vWf is measured in disease states.