VIIIR; Ag in platelets from patients with various forms of von Willebrand's disease.

Thirty patients with various forms of von Willebrand's disease were investigated for VIIIR:Ag in their platelets. VIIIR:Ag was extracted from washed platelets and measured both with electroimmunoassay and a sensitive immunoradiometric assay. Six patients had severe von Willebrand's disease, type I, with very low or no VIIIR:Ag in their plasma. None of these patients had any VIIIR:Ag detectable in their platelets. All 19 patients with mild von Willebrand's disease had VIIIR:Ag in their platelets but the values often fell below those of normal controls. Five patients with genetic variants of von Willebrand's disease also had values in their platelets corresponding to those in plasma.