Changes in Immature Reticulocytes Aid the Indirect Detection of Microdose Recombinant Erythropoietin Use in Men and Women

BREENFELDT ANDERSEN, A., J. BEJDER, T. C. BONNE, J. GRAAE, S. SEIER, and N. B. NORDSBORG. Changes in Immature Reticulocytes Aid the Indirect Detection of Microdose Recombinant Erythropoietin Use in Men and Women. Med. Sci. Sports Exerc., Vol. 55, No. 9, pp. 1695-1705, 2023. Purpose: We investigated whether immature reticulocyte fraction (IRF) and the immature reticulocytes to red blood cells ratio (IR/RBC) are sensitive and specific biomarkers for microdose recombinant human erythropoietin (rHuEPO) and whether the inclusion of reticulocyte percentage (RET%) and the algorithm "abnormal blood profile score (ABPS)" increased the athlete biological passport (ABP) sensitivity compared with hemoglobin concentration ([Hb]) and the OFF-hr score ([Hb]-60 x root RET%). Methods: Forty-eight (female= 24,male= 24) participants completed a 2-wk baseline period followed by a 4-wk intervention period with three weekly intravenous injections of 9 IU center dot kg- 1 center dot bw- 1 epoetin ss (female = 12,male = 12) or saline (0.9% NaCl, female= 12,male= 12) and a 10-d follow-up. Blood samples were collected weekly during baseline and intervention as well as 3, 5, and 10 d after treatment. Results: The rHuEPO treatment increased [Hb] (time-treatment, P < 0.001), RET% (time-treatment, P < 0.001), IRF (time-treatment, P < 0.001) and IR/RBC (time-treatment, P < 0.001). IRF and IR/ RBC were up to similar to 58% (P < 0.001) and similar to 141% (P < 0.001) higher compared with placebo, and calculated thresholds provided a peak sensitivity across timepoints of 58% and 54% with similar to 98% specificity, respectively. To achieve >99% specificity for IRF and IR/RBC, sensitivity was reduced to 46% and 50%, respectively. Across all timepoints, the addition of RET% and ABPS to the ABP increased sensitivity from 29% to 46%. Identification of true-positive outliers obtained via the ABP and IRF and IR/RBC increased sensitivity across all timepoints to 79%. Conclusions: In summary, IRF, IR/RBC, RET% and ABPS are sensitive and specific biomarkers for microdose rHuEPO in both men and women and complement the ABP.