Reliability of cystatin C in estimating renal function in rugby players

Dear Sir, Serum creatinine concentrations in professional athletes are higher than those found in the general population, as demonstrated in a large series of top-level sportsmen competing in eight different sports disciplines. Cystatin C has been proposed as an alternative to creatinine for assessing glomerular filtration rate (GFR). We measured serum creatinine concentration in 25 men (age range 22–30 years; mean body mass index [BMI] 27.4 (SD 1.3) kg/m) belonging to the Italian national rugby team; blood was drawn in January, in the middle of the competitive season, when the psychophysical stress for athletes is at highest level. Serum creatinine was measured by the Jaffe reaction (Aeroset c8000, Abbott, Chicago, IL, USA; upper limit of normal 110 mmol/L) and by an enzymatic method (Johnson and Johnson Vitros 950, Johnson and Johnson, Raritan, NJ, USA). Cystatin C was measured nephelometrically (Dade Behring, Marburg, Germany; upper limit of normal 0.95 mg/L). The mean Jaffe serum creatinine concentration was 115 mmol/L (SD: 13.3), while the mean value using the enzymatic method was 119 mmol/L (SD: 13.3). Twelve/fifteen players had serum creatinine concentrations exceeding 110 mmol/L using the Jaffe/enzymatic assays respectively. The mean cystatin C concentration was 0.85 mg/L (SD: 0.08); no player had a cystatin C concentration exceeding 0.95 mg/L. Body mass and in particular muscle mass are known to influence serum creatinine concentration. Our data suggest that serum cystatin C concentration may be a more accurate reflection of GFR in these professional athletes.