The effect of acute running exercise on plasma volume marker levels

When analyzing athletes' athlete biological passports (ABP), hydration, environmental factors, and the type of exercise are key variables that must be considered. A reduction in plasma volume (PV) after exercise can lead to elevated blood parameters and cause misinterpretations during ABP evaluations; therefore, understanding PV changes is essential. Current PV calculations rely on whole blood, which has limitations regarding transport and storage. This highlights the need for a serum marker that can reflect PV changes during ABP evaluations. A limited number of studies in the literature suggest that albumin and calcium can be used for this purpose. This study investigated whether serum markers could serve as a reference marker for ABP evaluations in a much larger participant group than previous studies. A total of 31 recreational athletes, who run at least three times a week, performed their routine one-hour running training. Blood and serum samples were collected before the run (t0), immediately after (t1), and two hours post-exercise (t2). PV changes were calculated using the Dill and Costill method from blood samples. Serum levels of albumin, calcium, transferrin, total protein, high-sensitivity CRP, LDL, and creatinine were measured, and correlations between PV changes and serum marker variations were analyzed. According to the results, PV decreased by 3% at t1 compared to t0 and increased by 6.2% at t2 compared to t1. Similarly, concentrations of albumin, total protein, and calcium initially increased and then decreased; however, when adjusted for PV, these markers exhibited a linear increasing trend. None of the serum markers showed a strong correlation with PV changes (r < 0.600), but albumin was the only marker that displayed a moderate and significant correlation with PV changes in all three samples (p < 0.05). These findings demonstrate that the markers evaluated in this study are insufficient on their own to reflect PV changes and suggest that incorporating a reference marker to indicate PV changes during ABP evaluation is not appropriate.