ABSTRACTBERGLUND, B., G. BIRGEGÅRD, L. WIDE, and P. PIHLSTEDT. Effects of blood transfusions on some hematological variables in endurance athletes.Med. Sci. Sports Exerc., Vol. 21, No. 6, pp. 637–642, 1989. Selected hematological variables (blood hemoglobin concentration [Hb], serum (s-) iron, s-bilirubin, s-ferritin, blood lactate, and s-erythropoietin [Epo]) were analyzed before and for 4 wk after autologous blood transfusions. A group of well-trained (8 male and 4 female) former endurance athletes was phlebotomized and 3–4 months later reinfused with the freezer-stored autologous red blood cells (RBC) from 1350 ml of blood. The [Hb] increased significantly (P< 0.001 for both sexes) from 146.7 ± 5.31 and 131.7 ± 11.20 g ± 1-1immediately before reinfusion to maximum values of 163.5 ± 7.47 and 155.9 ± 11.43 g ± 1-1(mean ± SD) in males and females, respectively, 2 d after reinfusion. S-iron increased transiently 5 h after reinfusion. S-bilirubin remained unchanged throughout the study. S-ferritin increased gradually (P< 0.02) from 48 ± 32.91 mmol ± 1-1before reinfusion to a maximum of 80.8 ± 39.52 mmol ± 1-12 wk after reinfusion. S-[Epo] increased transiently (P< 0.01) from 8.83 ± 2.51 (mean ± SD) to 12.36 ± 5.64 U ± 1-1, (mean ± SD) 5 h after reinfusion. Subsequently, there was a significant marked decrease in s-[Epo] to 5.85 ± 1.32 U ± 1-1, (mean ± SD) 1 d after reinfusion(P< 000.1, as compared to before reinfusion). Thereafter, s-[Epo] remained low throughout the study. Blood lactate was significantly decreased only the first 2 d after reinfusion (P< 0.05). An increase in [Hb] > 5% and a decrease in s-[Epo] of 30% was noted in 8/12 (75%) of the athletes after 1 wk and 3/12 (25%) after 2 wk. In conclusion, an algorithm based on an increase in [Hb] and a decrease in s-[Epo] might indicate blood transfusion with autologous freezer-stored RBC. However, the transfusion-induced decrease in s-[Epo] in subjects with normal s-[Epo] is relatively small, and it is doubtful whether the suggested algorithm can be used to indicate unequivocally a connection between blood transfusions and an individual athlete.