An immunological cross-reactant of erythropoietin in serum which may invalidate EPO radioimmunoassay

Mechanisms of anemia in CKD

Anemia is a common feature of CKD associated with poor outcomes. The current management of patients with anemia in CKD is controversial, with recent clinical trials demonstrating increased morbidity and mortality related to erythropoiesis stimulating agents. Here, we examine recent insights into the molecular mechanisms underlying anemia of CKD. These insights hold promise for the development of new diagnostic tests and therapies that directly target the pathophysiologic processes underlying this form of anemia.

Laboratory screening for erythropoietin abuse in sport: an emerging challenge

The growing diffusion of banned practice to improve the athletic performances is forcing clinical laboratories to identify and standardize reliable assays to detect potential unfairness. Among the doping practices, the use of recombinant human erythropoietin is becoming fairly popular, due to simplicity and safeties of administration and troublesome detection. The heterogeneous response rate, the presence of a little but significant amount of naturally occurring hormone, the short half-life exhibited by recombinant human erythropoietin and the lack of standardization of commercial assays appear the main problems to overcome. Aim of the present article is to provide a critical review of some of the more widespread laboratory techniques currently available for the screening for erythropoietin abuse in sport.

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.

Effect of iron on erythropoietin production in anaemic piglets

In the present study the response of plasma erythropoietin to iron injection in anaemic piglets was examined. At the age of 16 days, 4 piglets from the same litter were given 180 mg iron subcutaneously. After iron injection, blood samples for estimation of erythropoietin activity in plasma, haemoglobin concentration, and reticulocyte counts were taken every 6 or 12 h for 3 1/2 days. Plasma erythropoietin activity was estimated by a monoclonal enzyme-immunoassay (ELISA), developed for human erythropoietin. On the day of iron injection, haemoglobin concentration ranged between 41 and 48 g/l, reticulocyte counts from 9 to 17 percent, and plasma erythropoietin between 22 and 144 mU/ml. In 3 of the 4 piglets, iron injection resulted in a 2-6 fold increase in erythropoietin activity. Maximal erythropoietin activities were observed 24-42 h after injection, and after 66 h, the activities were close to the pretreatment values. It is concluded that in our experiment, iron, per se, has stimulated erythropoietin production.

Correlation between a sandwich ELISA and an in-vitro bioassay for erythropoietin in human plasma

A sandwich-type enzyme-linked immunosorbent assay (ELISA) for human erythropoietin (EPO) using two anti-EPO monoclonal antibodies has been compared with an in-vitro EPO bioassay based on CFU-E colony formation in fetal mouse liver cell cultures. In normal subjects and non-uraemic anaemic patients the plasma EPO values estimated with the ELISA correlated well with those by the bioassay, and also inversely with the values of blood Hb, PCV and RBC counts. Dose-response curves for plasma and standard recombinant human EPO in the ELISA were parallel to each other. These results further confirm the validity for the ELISA in measuring circulating human EPO.

Regulation of erythropoietin production in a case of congenital erythropoietin-dependent pure erythrocytosis

In a patient with congenital erythropoietin-dependent pure erythrocytosis (EDPE) associated with hypersensitivity of erythroid progenitor cells to erythropoietin (Epo), the investigations planned to elucidate the mechanism responsible for hormone hyperproduction revealed that Epo synthesis was (1) independent of normal oxygen-mediated feedback induced by phlebotomy; (2) not modulated by adenosine as a second messenger (the treatment with the adenosine antagonist theophylline in fact left unchanged the serum Epo levels); and (3) uninfluenced by iron therapy. The Epo dose-response curve for growth of erythroid progenitor was similar to that of three age-matched thalassemia patients with increased serum Epo levels, (sEpo) suggesting that the observed erythroid progenitors hypersensitivity to Epo could represent an ex vivo artifact induced by the increased sEpo levels.

Inadequate erythropoietin response to anemia: definition and clinical relevance

The development of a specific and sensitive immunoassay for the measurement of serum erythropoietin (s-Epo) allows to improve our understanding of the model of in vivo regulation of erythropoiesis. In most anemias, circulating hemoglobin level determines Epo production which in turn stimulates erythropoietic activity. The disruption of the expected feedback mechanism of Epo production leads to an inadequately low s-Epo. The definition of inadequate Epo response to anemia relies on the documentation of a downregulated dependence of s-Epo on Hb with respect to the same dependence in patients with a physiologically regulated erythropoiesis. Literature reports a wide range of so called adequate s-Epo response to anemia and a number of criteria for judging on the adequateness of s-Epo at a certain degree of anemia. The O/P (observed/predicted) ratio allows categorization of each individual patient. The clinical syndromes in which an inadequate Epo response has been reported are numerous and the mechanisms of defective Epo production are different. A number of evidences clearly point to a relation between responsiveness to r-Hu-Epo and inadequate Epo response. This inequivocabily confirms the role inadequate Epo response plays in the pathogenesis of anemia.

Unreliability in immunoassays of erythropoietin: anomalous estimates with an assay kit

We report the finding of inappropriately high estimates of erythropoietin (Epo) in 11% of serum samples tested by one commercial assay kit. These estimates were not confirmed when the same samples were tested independently in four other systems for the immunoassay of Epo. As yet no explanation has been found to account for the anomalously high estimates.

Improved microbioassay for plasma erythropoietin based on CFU-E colony formation

We examined the conditions necessary for performing a reliable erythropoietin (EPO) assay based on CFU-E colony formation in fetal mouse liver cell (FMLC) microcultures using 96-well microtiter plates. Both linearity of colony numbers with the number of cells plated and comparison among the colony ratios at various densities of seeding cells indicated that the colonies originated from a single progenitor cell when 7500 or fewer cells were plated into individual microtiter wells. About a twofold CFU-E enrichment in 12- to 13-day FMLC was achieved by Ficoll-Paque centrifugation. Plasma treated with acid-boiling stimulated the colony formation most and contained no colony inhibitor. Dose-response curve for the plasma was parallel to the EPO standard curve. The "erythroid colony-stimulating activity" in the plasma was additive to that in the standard EPO, and was completely neutralized by a monoclonal antibody against recombinant human EPO. Using the assay procedure thus established, plasma EPO titer was determined in normal subjects, in patients with nonuremic anemia and polycythemia vera, and in dialysis patients with chronic renal failure. The use of different preparations of standard EPO resulted in a significant difference in the titers because their dose-response curves differed from one another. An inverse relationship was found between EPO titers and hemoglobin concentrations in the nonuremic anemic patients, but not in the dialysis patients with about one half the normal EPO level.

Assessment of an EIA for measuring human serum erythropoietin as compared with RIA and an in-vitro bioassay

A recently developed enzyme-linked immunosorbent assay (EIAZ, ELISA) using two murine monoclonal anti-erythropoietin antibodies was compared with a radioimmunoassay (RIA) and a commercial in-vitro bioassay, EPOS, for measuring serum erythropoietin (Epo) in humans. Specificity and validity for Epo-EIA and the other two assays were examined. The serum Epo in normal subjects was 18 +/- 12 mU/ml (mean +/- SD, n = 80) for EIA compared with 22.5 +/- 18.5 mU/ml (n = 20) for RIA and 136 +/- 132 mU/ml (n = 14) for the bioassay. The serum Epo concentrations in normals and patients were highly comparable between EIA and RIA for Epo (P less than 0.01, r = 0.95). Epo concentrations by the EIA for normal female and male subjects were 20.5 +/- 13 and 16.5 +/- 10 mU/ml, respectively. Epo levels in patients with secondary polycythaemia or autoimmune haemolytic anaemia were significantly higher than normal subjects by the three methods. Epo levels in patients with chronic renal failure were within the normal range. By the EPOS bioassay, the Epo concentrations of normals and patients with renal failure were significantly higher than expected (136 +/- 132 and 447 +/- 273, respectively). Due to its inherent design, the EPOS bioassay possibly measures bone marrow proliferative activity in response to other serum growth regulators besides erythropoietin and was found to be unsuitable for clinical assessment of Epo. We concluded that the new EIA and RIA were similarly sensitive, reliable and accurate for measurement of serum Epo. The EIA method has the advantage of being less time consuming, more convenient and avoids the use of a radioisotope.

Comparisons of human, rat and mouse erythropoietins by isoelectric focusing: differences between serum and urinary erythropoietins

Isoelectric focusing (IEF) in the pH range 2.5-5.0 has been used to compare the immunoreactive (ir) erythropoietin (Epo) in paired samples of serum and urine from three patients, two with idiopathic aplastic anaemia and one with paroxysmal nocturnal haemoglobinuria and also from three anaemic rats. Serum samples only were also examined from two further patients with aplastic anaemia and from three mice, made anaemic (like the rats) by irradiation and phenylhydrazine treatment. Most of the ir-Epo recovered after IEF was found in the pH range 2.5-3.9. For the sera, the proportion of more acidic ir-Epo with pI less than 3.0 recovered after IEF increased from human to rat to mouse. Human sera contained a greater proportion of ir-Epo with pI greater than 3.4 than rat or mouse sera. For the urines, the distribution of ir-Epo by IEF was similar between human and rat. For both species, the proportion of ir-Epo with pI less than 3.0 recovered after IEF was greater in urine than in the paired serum samples. The Second International Reference Preparation of Human Urinary Epo differed from the Epo in unextracted human urine in that there was a lower proportion of ir-Epo with pI less than 3.0. The differences observed between serum and urinary Epo are of particular interest because only the urinary form of native human Epo has ever been purified, and because this was used to compare native with rDNA-derived Epo.