Background An elevated platelet count may lead to an increased incidence of systemic thromboembolism or unexpectedly to thrombohemorragic complications.

Both, incidences of systemic thromboembolism and unexpected thrombohemorragic complications (bleeding) were described in patients with an elevated platelet count.

In the present study the quantitative hemostatic indices were measured in 46 patients with thrombocytosis (platelet count > 400.000 per microliter), including 23 patients with secondary thrombocytosis (17 patients with rheumatoid arthritis, 2 with lung cancer, 1 with systemic lupus erythematosus, 1 with granuloma Wegeneri) and 23 patients with myeloproliferative thrombocytosis (12 with chronic myeloid leukaemia, 8 with polycythemia vera, 3 with idiopathic thrombocytosis).

In both studied groups, von Willebrand factor activity and epinephrine-induced platelet aggregation were decreased, and activated partial thromboplastin time was prolonged, thus, suggesting increased risk of bleeding complications.

On the other hand, the concentrations of fibrinogen and d-dimmers were enhanced and bleeding time was shortened. These findings argue for an enhanced risk of thrombosis.

Since no differences between two studied groups were found, it seems that the observed abnormalities were directly related to the elevated platelet count and were not associated with primary disease.

The low incidence of hemostatic complications in patients with secondary and myeloproliferative thrombosis may suggest that the coexistence of an additional component is critical for the clinical manifestation of such disturbances.