RESUMEN
BACKGROUND: Von Willebrand factor (vWf) plays a crucial role in the early phase of hemostasis. Acquired von Willebrand disease (vWD) due to abnormalities of vWf multimers has been reported in patients with myeloproliferative disorders (MPD) who have high platelet counts. We compared the distribution of plasma vWf antigen and large vWf multimers in samples obtained from patients with MPD and reactive thrombocytosis (RT). Furthermore, we tried to find the relationship between the decrease of large vWf multimers in plasma and the bleeding complication. METHODS: Sixteen patients with MPD and twenty-five patients with RT with more than 600x103/microliter of platelets were included in the study. The numbers of platelets and leukocytes, platelet distribution width (PDW), mean platelet volume (MPV), platelet-large cell ratio (P-LCR), vWf : Ag and vWf multimers were measured. RESULTS: The mean values of platelets and leukocytes were 1,091x103/microliter, 82.9x103/ in MPD and 763x103/, 11.4x103/ in RT (P<0.05). Platelet parameters such as MPV,PDW, P-LCR were 11.2 fL, 10.2%, 28.6% in MPD, and 9.6 fL, 9.9%, 19.6% in RT (P<0.05). The levels of vWf : Ag and large vWf multimer were 120.8 U/dL, 13.8% in MPD and 184.3 U/ dL, 20.7% in RT (P<0.05). Large vWf multimers were decreased in 11 MPDs and 2 RTs. Bleeding diathesis appeared only in 2 MPDs with decreased large vWf multimers. Platelet or leukocyte count was inversely correlated with large vWf multimers, but vWf antigen was correlated with large vWf multimer. CONCLUSION: The findings of normal vWf antigen level and decreased percentage of large vWf multimers are more frequent in MPD than in RT, and the measurement of these parameters is useful to differentiate MPD from RT. Bleeding complication in the patients with MPD with decreased large vWf multimers might be prevented by correction of decreased large vWf multimers.