Anomalies in circulating erythropoietin levels

Are current methods of measurement of erythropoietin (EPO) in human plasma or serum adequate for the diagnosis of polycythaemia vera and the assessment of EPO deficiency?

Current methodology for the immunoassay of erythropoietin (EPO) in human plasma or serum is reviewed, with an emphasis on measurement of EPO concentrations in the low and normal ranges, analytical interference and blood sampling requirements. In only 2 out of 8 research or in-house immunoassays reported since 1987 was there evidence that patients with polycythaemia vera (PV) could be identified, PV being an EPO-independent form of polycythaemia in which EPO concentrations are low in untreated cases. The same was true for only 1 out of 13 currently available kit methods. Remarkable differences in sample stability have been observed with different methods. Measurement of EPO in serum is recommended in most published articles. However, only EDTA plasma seems to be acceptable for the one generally available method with proven high diagnostic sensitivity for PV. It is concluded that most EPO assay methods have not been shown to be adequate for the measurement of the low EPO concentrations, and thus have poor diagnostic sensitivity for PV. It is inferred that they might not be appropriate to assess states of EPO deficiency. Only when a sufficiently sensitive diagnostic method becomes generally available will it be possible to define the various causes of low EPO concentrations. As in other fields of polypeptide hormone measurement, further developments in the field of EPO assay may be expected to be important in diagnostic medicine.

Plasma erythropoietin by high-detectability immunoradiometric assay in untreated and treated patients with polycythaemia vera and essential thrombocythaemia

By using an immunoradiometric method with a stated detection limit of < or =1 IU/l (stated normal reference limit in adults 3.7-16 IU/l) we determined EDTA-plasma erythropoietin (EPO) in 58 patients with polycythaemia vera (PV) and 49 patients with essential thrombocythaemia (ET). At the time of blood sampling, 20 of the PV patients were newly diagnosed and untreated, 23 were treated by phlebotomy only, and 30 also received myelosuppressive treatment (with 32P, hydroxyurea or alpha-interferon). Of the ET patients 24 were untreated and 28 received myelosuppressive therapy. For comparison plasma EPO was also determined in 10 patients with pseudopolycythaemia (PP). In this latter group the results for plasma EPO agreed well with the cited normal reference limits. The majority of untreated PV patients (12/20) had undetectable plasma EPO concentration, and the remainder all had values below the lower normal reference limit. Plasma EPO in PV was not significantly influenced by phlebotomy therapy. Twelve of the 24 untreated ET patients (50%) had plasma EPO values below the reference interval (undetectable in 2 patients). The mean EPO concentration was significantly lower in PV patients receiving phlebotomy therapy than in patients with untreated ET. In the total material of PV and ET treated with myelosuppressive agents the PV patients showed significantly lower values for EPO concentration than did patients with ET. The present results support the view that EPO measurements by high-detectability methods are diagnostically useful and should be included in the panel of new criteria for the diagnosis of PV.