Reticulocyte parameters as potential discriminators of recombinant human erythropoietin abuse in elite athletes

This study investigated using reticulocyte (retic) parameters as indirect m arkers of human recombinant erythropoietin (r-HuEPO) abuse in elite athlete s. Absolute reticulocyte count (# retic), the per cell haemoglobin content of reticulocytes (CHr), reticulocyte haemoglobin mass per litre of blood (R etHb) and red blood cell:reticulocyte haemoglobin (RBCHb:RetHb) ratio were assessed using flow cytometry. Venous blood was drawn from 155 elite athlet es from six sports during regular training to establish reference ranges (9 5% confidence interval) for these parameters. The reference ranges were com pared with those of a non-athletic population (n = 23), four groups of athl etes (n = 24) before and after exposure to simulated altitudes (2500-3000 m for 11 - 23 nights), two groups of elite cyclists (n = 13) before and afte r four weeks of training at natural altitude (1780 and 2690 m), and with th ose of non-athletic subjects from a separate study (n = 24) before and 1-2 days after they were injected with 1200 U x kg(-1) r-HuEPO over a 9-10 day period. Generally the changes induced by r-HuEPO injection exceeded by appr oximately 100% the magnitude of the changes associated with natural altitud e exposure. Simulated altitude exposure did not significantly alter the ret iculocyte parameters. From the sample of 155 non-users and 24 r-HuEPO users , the population mean and variance, as well as the 95% confidence limits fo r the population mean and population variance, were estimated. Relative to arbitrarily chosen cut-off levels, the confidence limits for the rate of tr ue positives and rate of true negatives were also calculated. Based on the lowest rate of false positives and highest rate of true positives, the best discriminator between r-HuEPO users and non-users was # retic, marginally superior to RBCHb:RetHb ratio and RetHb. At a cut-off for # retic of 221 x 10(9) x L-1 we could be 95% sure that we would find no more than 7 false po sitives in every 100 000 tests. We would expect to pick up 51.8% of users, and could be 95% sure of picking up at least 38% of current or recent users . This result highlights the potential power of retic parameters for detect ing r-HuEPO abuse among athletes. However, the efficacy of these cut-offs f or detecting r-HuEPO abuse is unknown if an athlete is a chronic user or st ops using r-HuEPO several weeks before being tested.