The relation between plasma thrombopoietin and erythropoietin concentrations in polycythaemia vera and essential thrombocythaemia

Plasma thrombopoietin (TPO) was measured, by immunoenzymometric assay, in 39 patients with polycythaemia vera (PV), 33 patients with essential thrombocythaemia (ET) and 10 healthy volunteers. The mean TPO concentration was significantly higher in ET patients than in PV patients (p=0.04) and normals (p <0.001). The 6 untreated ET patients had a significantly lower mean TPO concentration compared to the 27 ET patients who were on myelosuppressive regimens (p=0.01). The mean plasma TPO for the 5 PV patients treated with phlebotomy only did not differ significantly from the corresponding mean for the 34 PV patients treated with myelosuppressive agents. Concomitantly, plasma EPO was measured in 25 of the PV patients and in 30 of the ET patients by an immunoradiometric assay with normal reference interval in adults 3.7-16 IU/L. In the 14 PV patients with EPO <3.7 IU/L mean plasma TPO did not differ significantly from the mean for the II PV patients with EPO greater than or equal to3.7 IU/L; neither of these two groups had plasma TPO concentrations significantly different from the mean for the control subjects. The 7 ET patients with subnormal plasma EPO had significantly lower mean plasma TPO compared to the ET patients with normal and high plasma EPO concentrations (p=0.03 and p=0.02, respectively). Also, the 16 ET patients with normal plasma EPO had significantly lower plasma TPO compared to the 8 patients with high plasma EPO (p=0.04). The mean plasma TPO for each of these three groups of ET patients was significantly higher than the corresponding mean for the controls (p <0.001 for each group). The results of the present study indicate that a relationship between plasma EPO and TPO concentrations may exist and that myelosuppressive treatment affects the TPO concentration in ET but not in PV patients.