Circulating thrombopoietin in clonal versus reactive thrombocytosis.

INTRODUCTION: The aim of this study is to assess circulating thrombopoietin concentrations in patients with both clonal and reactive thrombocytosis (RT), which are two distinct categories of extreme platelet production circumstances. Investigation of the thrombopoietin levels in clonal versus reactive thrombocytosis may help us to understand the interactions of this key regulatory cytokine and the conditions in which abnormally increased platelet formation exist.
MATERIALS AND METHODS: Thrombopoietin levels were measured in patients with platelet counts greater than 500 x1 0(3) microl(-1). The study population consisted of 21 patients with RT (13 with iron deficiency anemia, and 8 with rheumatoid arthritis), 24 patients with clonal thrombocytosis (six with essential thrombocytosis, three with myelofibrosis, eight with chronic myelogenous leukemia, and seven with polycythemia vera (PV)) and 16 healthy subjects were used as controls.
RESULTS: The median plasma thrombopoietin concentration was 100.5 pg ml(-1) in patients with RT, 467 pg ml(-1) in patients with clonal thrombocytosis and 62.65 pg ml(-1) in the control group. The thrombopoietin concentration was found to be higher in the patients with primary thrombocytosis when compared to the control group (p=0.001), as well as in patients with RT (p=0.002). However, there was no statistically significant difference between the patients with RT and the control group (p=0.14). There was no correlation between thrombopoietin levels and the platelet counts in patients with clonal thrombocytosis, including essential thrombocythemia (ET). CONCLUSIION: Increased levels of thrombopoietin were found in patients with clonal thrombocytosis versus patients with RT and control subjects as well. Defective clearance of thrombopoietin by megakaryocytes and platelets due to a reduced number of thrombopoietin receptors may be the causative mechanism behind this. These results indicate that plasma thrombopoietin levels may be helpful in distinguishing between clonal and reactive thrombocytosis.