How to Evaluate Kidney Function in Elite Endurance Athletes: Pros and Cons of Different Creatinine-Based Formulas

Background: Various creatinine-based equations are used to estimate the glomerular filtration rate (eGFR) in athletes, but each has limitations. The aim of our study was to identify the most suitable formula for use in athletes. Methods: We evaluated 490 Olympic athletes (27 ± 5.3 yo) with normal values of serum creatinine and no history of kidney diseases. Athletes were divided into those practicing skills and endurance disciplines. The EGFR was calculated with Cockcroft-Gault (CG), MDRD, MCQE and CKD-EPI, and classified as stages G1-G5 according to the Kidney Disease Improving Global Outcomes (KDIGO) GFR categories. Results: Endurance athletes showed higher serum creatinine (0.91 ± 0.14 mg/dL vs. 0.88 ± 0.13 mg/dL in skills, p = 0.014). The eGFR calculated with the CKD-EPI and MCQE formulas showed no differences between the groups. The CG formula produced a lower eGFR for endurance athletes (113.6 ± 27 mL/min/1.73 m²) compared to skills athletes (122.6 ± 30.8, p = 0.008), while MDRD produced higher values for endurance athletes (129.3 ± 25.8 vs. 122.6 ± 24 mL/min/1.73 m², p = 0.004). According to CKD-EPI, all athletes were in G1, while with MCQE, 0.5% of skills athletes and 1% of endurance athletes were in G2. With the CG formula, a significant percentage of athletes were in G2 (13.2% of skills athletes and 18.5% of endurance athletes, p = 0.125). With the MDRD formula, 29 athletes (5.9%) were in G2 (6% for skills athletes and 5.8% for endurance athletes, p = 0.927). Conclusions: CKD-EPI and MCQE showed better stability and reliability, making them the most suitable for kidney function evaluation in athletes.