2.1.4. sCyst-C is a Better Marker of eGFR than sCr

Interesting observations were made in nine professional cyclists during the Giro d'Italia. In this study, blood was taken before, on the 12th and on the 22nd day of the race. The mean sCyst-C remained very stable: 0.61 ± 0.06 vs 0.62 ± 0.07 vs. 0.63 ± 0.06 mg/L. In this very interesting study, which is described in detail in two papers [28,29], blood was not taken immediately after the single race. Therefore, the study is not exactly in the scope of this review. Nevertheless, it provided evidence that even one of the most exhausting multistage efforts does not lead to an eGFR decrease in healthy, well-trained sportsmen [28,29]. Studies published by Banfi and Colombini showed that in athletes, sCyst-C is a better marker of eGFR than serum creatinine (sCr), also at rest. Some athletes, like cyclists, have a creatinine level that is lower than the reference values, due to a low lean mass (e.g., 9/9 cyclists

taking part in the Giro d'Italia), while 12/15 professional rugby players had serum creatinine above the reference values due to their high body mass. In both of these studies, athletes had levels of serum Cyst-C in the normal range [28–30].

sCyst-C is also more precise than a sCr marker of eGFR in studies in which lean body mass is changing. In a study of a 6-month physical activity program in obese boys, serum creatinine increased, but sCyst-C remained unchanged. In the subjects, the lean mass and height increased, while their weight did not change [31].
