Human thrombopoietin levels are high when thrombocytopenia is due to megakaryocyte deficiency and low when due to increased platelet destruction.

Megakaryocyte mass, reflected in the rate of platelet production, appears to be the major determinant of TPO levels in thrombocytopenic patients rather than circulating platelet levels per se, and measurement of serum TPO may be useful in differentiating thromBocytopenias due to peripheral destruction from those due toThrombopoietic failure.