Thrombocytosis and thrombocythemia: qualitative platelet abnormalities.

Thrombocytosis occurs as a primary disease of the bone marrow (primary thrombocytosis or thrombocythemia) or as a reactive phenomenon in pathologic and physiologic conditions (secondary thrombocytosis or thrombocytosis in a narrow sense). As a rule, secondary thrombocytosis is symptomless and shows normal platelet functions, while thrombocythemia is frequently associated with bleeding and/or thrombosis as well as various platelet abnormalities. These platelet abnormalities were reviewed, and our recent studies on functional and biochemical alterations in platelets of thrombocythemia were focused on: 1) abnormal platelet aggregation. 2) deficient epinephrine-induced elevation of the cytoplasmic Ca2+ concentration in platelets with defective aggregation response to epinephrine, 3) altered (subnormal and increased) platelet responses to thromboxane A2 (abnormal thromboxane A2 receptor), and 4) abnormal platelet 12-lipoxygenase enzyme. Although the clinical significance of the in vitro qualitative platelet defects is not always clear, these altered platelets could be useful models to elucidate platelet pathophysiology.