Does body position before and during blood sampling influence the athlete biological passport variables?

The Athletes Biological Passport (ABP) is a tool for the indirect detection of blood doping. Current guidelines from the World Anti-Doping Agency (WADA) require a delay of 2 hours after any physical exercise and to be seated for 10 minutes prior to any blood sampling to obtain a valid measurement. Since body position prior to and during phlebotomy may influence the outcome, this study compared blood biomarker variations with changes in body position during blood sample collection. Ten successive venous blood samples from 38 subjects of 3 groups (elite cyclists, apnea divers and controls) in three situations (seated, after a 50 m walk, and supine) were collected and analyzed via flow cytometry. While reticulocytes percentage was unchanged in all conditions, haemoglobin concentration and hematocrit were stable after at least 10 min in a seated position. Due to shifts in plasma volume, the measures were significantly higher after changing posture for a short walk, but readjusted to previous levels after only 5 min. Supine position caused generally lower values after 10-30 min. The results support the current guidelines and additionally provide evidence to adjust the waiting time for blood sampling after short changes in posture.