Activated Protein C Resistance in Polycythemia Vera

Activated protein C resistance is a result of a point mutation in factor V gene (Leiden mutation) and can be identified in approximately 50% of patients with thrombosis, making it an important risk factor for thrombosis. The aim of this study is to evaluate the role activated protein C resistance in the hypercoagulable state seen in polycythemia vera. We compared patients with polycythemia vera (n: 24) for increased risk of thromboembolism and activated protein C resistance, with the results of patients with chronic myelogenous leukemia (n: 27) and healthy control group (n: 52). Activated protein C resistance test and factor VIII activity was determined by an aPTT based test. Anticardiolipin antibodies IgG and IgM were also determined by ELISA. Leiden mutation was studied with polymerase chain reaction. Venous thromboses were observed in 12.5% and arterial thromboses in 41.6% of patients with polycythemia vera. Arterial thromboses were recognized in 7.4% of patients with chronic myelogenous leukemia. Activated protein C resistance was identified in 20.8% of patients with polycythemia vera and 14.8% with chronic myelogenous leukemia (versus 1.8% of healthy control subjects). The risk of thrombosis in patients with polycythemia vera was independent from the presence of activated protein C resistance. Leiden mutation was observed in only 1 patient out of 4 patients with chronic myelogenous leukemia who had activated protein C resistance, but not thrombosis. Factor VIII levels of patients with chronic myelogenous leukemia (158% ± 14) were higher than healthy control subjects (99% ± 15) (p< 0.05). Patients with activated protein C resistance in both groups had no seropositivity for anticardiolipin antibodies IgG and IgM. Activated protein C resistance and in some cases its association with Leiden mutation in polycythemia vera may not have a major role in the pathogenesis of thromboembolic complications of polycythemia vera.