Patients with thrombocytosis have normal or slightly elevated thrombopoietin levels.

BACKGROUND AND OBJECTIVE The distinction between clonal and reactive thrombocytoses is a frequent problem and implies different therapeutic options. As thrombopoietin (TPO) is the main regulator of megakaryocytopoiesis and thrombopoiesis, we measured TPO levels in patients with thrombocytosis in an attempt to understand the regulation and potential utility of distinguishing thrombocytoses. DESIGN AND METHODS Serum TPO levels, platelet counts, mean platelet volume, hemoglobin, erythrocyte sedimentation rate and age were evaluated in 25 patients with clonal thrombocytosis (15 with essential thrombocythemia, 6 with polycythemia vera and 4 with chronic myeloid leukemia) and in 50 patients with reactive thrombocytosis distributed in three groups: 1) patients in post-surgical states; 2) patients with solid tumors; and 3) patients with inflammatory diseases. RESULTS TPO levels were slightly increased in patients with clonal (135+/-50 pg/mL) and reactive (147+/-58 pg/mL) thrombocytosis compared with controls (121+/-58 pg/mL). Analyzing the different groups, patients with essential thrombocythemia had the lowest TPO levels (120+/-28 pg/mL) and patients with solid tumors the highest levels (162+/-59 pg/mL). Patients with clonal thrombocytosis were older, had higher platelet counts, mean platelet volume and hemoglobin, and lower erythrocyte sedimentation rate than patients with reactive thrombocytosis. INTERPRETATION AND CONCLUSIONS Minor differences were observed in TPO levels between patients with primary and secondary thrombocytoses. Erythrocyte sedimentation rate, but not TPO levels, may be a useful tool for discriminating both types of thrombocytoses.