Platelet von Willebrand Factor in Patients with von Willebrand Disease Type I: Preliminary Report
Platelet von Willebrand Factor (vWF) was studied in normal donors (n = 10) and in patients with von Willebrand disease (vWD) type I (n = 12). The vWF antigen (Ag) and the functional parameter, measured as the vWF collagen binding activity (CBA), were determined by parallel quantitative ELISAs. In the platelets of normal donors the concentrations (mean±SD) of Ag and CBA were 0.40 ±0.18 U/109 platelets and 0.44 ± 0.24 U/109 platelets, respectively, with a CBA to Ag ratio of 1.06 ±0.17. There was no correlation between the plasma concentrations of Ag and CBA with those in platelets either in normal donors or in patients with vWD type I. On the basis of their concentrations of Ag and CBA in platelets, patients could be subdivided into two groups: (1) platelet normal, i.e. those with a normal Ag and CBA content of 0.35±0.18 U/109 platelets and 0.42±0.21 U/109 platelets, respectively, and (2) platelet low/discordant, i.e. those with a low Ag and CBA content of 0.15±0.06U/109 platelets and 0.07±0.03 U/109 platelets, respectively. Patients with “platelet low/discordant” vWF content had an increased bleeding tendency when compared to those patients with “platelet normal”, confirming the relevance of platelet vWF in haemostasis.
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