A multi-parametric approach to remove the influence of plasma volume on the Athlete Biological Passport during a UCI cycling stage race.

Fluctuations in plasma volume (PV) present potential confounders within the concentration-based markers of the hematological Athlete Biological Passport (ABP). Here, a multi-parametric approach involving a simple blood test is applied to the current ABP adaptive model in an attempt to remove the influence of PV expansion, induced by a cycling stage race. Blood samples were obtained from 29 professional cyclists (15 female, 14 male) before, during, and after 4-5 consecutive days of racing. Whole blood was analysed in accordance with the World Anti-Doping Agency ABP guidelines for haemoglobin concentration ([Hb]) and platelets. Serum and plasma were analysed for transferrin, albumin, calcium, creatinine, total protein, and low-density lipoprotein. PV variation (Z-scores) was estimated using a multi-parametric model (consisting of the bio-markers above) and compared against calculated variations in PV (measured via CO-rebreathing). Significant reductions in [Hb] and the OFF-score were observed in females after 3 and 4 days of racing, with accompanying increases in PV, which returned to baseline values 4 days post competition. Similarly, a significant increase in PV was observed in males after 3 and 5 days of racing. When individual estimations of PV variance were applied to the adaptive model, the upper and lower reference predictions for [Hb] and the OFF-score were refined such that all outliers consistent with racing induced PV changes were removed. The PV model appears capable of reducing the influence of PV on concentration-dependent markers during competition. This is an important step towards the inclusion of the PV correction in the ABP hematological module.