The red cell mass, plasma erythropoietin and spleen size in apparent polycythaemia

Oxygen affinity is decreased in patients with polycythaemia vera and essential thrombocythaemia

The plasma erythropoietin (EPO) concentration is subnormal in the vast majority of all patients at the time of diagnosis of polycythaemia vera (PV) and in 33-50% of patients with essential thrombocythaemia (ET). At equivalent haemoglobin concentrations patients with PV and a substantial number of ET patients have subnormal EPO concentrations compared with those of healthy subjects. A possible explanation could be altered haemoglobin (Hb) oxygen affinity. Plasma EPO concentration and the oxygen pressure at 50% Hb saturation (p50) were measured in 29 patients with PV, 23 patients with ET and 34 healthy controls. There was no significant correlation between p50 and plasma EPO concentration. However, the mean p50 for PV patients exceeded the mean for healthy controls (p = 0.004). Furthermore, the mean p50 for ET patients significantly (p = 0.012) exceeded the mean for controls but there was no significant difference in p50 between patients with PV and ET. It could be hypothesized that the lower oxygen affinity to Hb in PV and ET patients partly explains the decreased EPO production.

Serum erythropoietin values in erythrocytoses and in primary thrombocythaemia

Serum erythropoietin (Epo) values were estimated in samples from 125 patients with erythrocytosis to examine the specificity and sensitivity of reduced and raised values in the diagnosis of polycythaemia vera (PV) and secondary erythrocytosis (SE) respectively. Additionally, Epo values were estimated in samples from 49 patients with primary thrombocythaemia (PT) to determine whether Epo values were altered. We found high specificity (92%) and moderate sensitivity (64%) of low serum Epo values (below the reference range) in the diagnosis of PV, and also poor sensitivity (47%) of raised Epo values in the diagnosis of SE. Raised Epo values were not observed in PV patients with Hb > 14.0 g/dl and were only observed in one PV patient with a relatively low Hb recovering from a gastro-intestinal haemorrhage. Raised Epo values occurred in some patients with apparent erythrocytosis (AE) and idiopathic erythrocytosis (IE), mainly at normal (rather than raised) Hb values (< 16 g/dl). Low Epo values occurred in a few AE, IE and SE patients at higher Hb values (> 16 g/dl). Low Epo values were less specific for PV when the Hb was raised, while raised Epo values were less specific for SE when the Hb was not raised. Approximately one third of patients with PT had a low (below the reference range) Epo value, this being associated with a high normal Hb (> 14 g/dl, P < 0.001) and showing a trend towards association with absence of treatment. The high normal Hb values were in turn associated with an increased incidence of thrombotic events (P < 0.05). These findings could influence the future investigation and management of PT patients.

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 11 PV patients with EPO >or=3.7 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.