APC resistance as an additional thrombotic risk factor in a patient suffering from polycythemia vera and recurrent thrombosis.

Patients with polycythemia vera (PV) have a high risk of thrombosis. However, thrombosis is not sufficiently predictable with standard diagnostic procedures. We report on a patient with PV and recurrent thrombosis who nevertheless had a low platelet count while under therapy with hydroxyurea. As a result of duodenal ulcer and gastrointestinal bleeding, treatment with phenprocoumon was stopped years ago. Recently, heterozygosity for the factor V gene defect was diagnosed and anticoagulation therapy was reconsidered. In conclusion, the presence of resistance to activated protein C was an additional thrombotic risk factor that was important for our decision to change the treatment strategy in our patient.