Increased von Willebrand factor levels in polycythemia vera and phenotypic differences with essential thrombocythemia

Background Acquired von Willebrand factor (VWF) deficiency was described in Philadelphia‐negative myeloproliferative neoplasms, especially in essential thrombocythemia (ET). VWF phenotype in contemporary patients with polycythemia vera (PV) remains less explored. Objectives To characterize the VWF phenotype in PV and to compare VWF phenotype in PV with matched healthy subjects and ET patients. Patients/Methods We studied 48 PV patients, treated according to current recommendations (hematocrit ≤ 45%, on low‐dose aspirin prophylaxis); 48 healthy and 41 subjects with ET, all sex, age, and blood group matched. We measured VWF antigen, activity, multimeric pattern, ADAMTS‐13, and factor VIII (FVIII) antigen. Results In patients with PV, VWF antigen and activity were significantly higher than in healthy subjects (antigen: 119[96‐137] vs 93[79‐107] IU/dL; activity: 114[95‐128] vs 90[79‐107] IU/dL, respectively, medians and interquartile, P