Creatinine: An Inaccurate Measure of Renal Function in Men with Testosterone-Induced Muscle Hypertrophy

Abstract

ABSTRACT Introduction Renal function is often estimated using validated study equations and serum creatinine (Cr) as a filtration marker. Contemporary studies suggest that cystatin C may be used as a more accurate alternative to Cr, as it avoids limitations related to diet and muscle mass that affect Cr and predispose to an overdiagnosis of chronic kidney disease. Elite athletes are often noted to have an elevated body mass index (BMI) despite maintaining an overall favorable level of percent body fat (PBF) and fitness. This is due to an increase level of body muscle. Objective This study evaluates the relationship between Cr, cystatin C, BMI, and PBF in fitness and elite athlete populations. Methods Elite athletes presenting to a men's health tertiary referral center with muscle-induced hypertrophy were evaluated for renal function through serum levels of Cr and cystatin C. BMI and PBF were obtained through bioimpedance testing at the time of serum level determinations. Elite athletes were those identified as pursuing competition in professional or amateur sporting events. Cr and cystatin c were plotted for correlation in best fit models for percentage increments of BMI (“normal”, “overweight”, and “obese”) and PBF. Results A total of 228 elite athletes were identified and stratified by BMI and PBF (Figures 1,2). The majority of athletes were classified as “overweight” (n = 88) or “obese” (n = 129) per BMI. None of the BMI groups demonstrated a significant correlation between Cr and cystatin C levels (Figure 1). The obese cohort demonstrated increased levels of cystatin C (mean = 1.00337, P<0.0001) compared with the overweight cohort (mean = 1.474462, p P<0.0001). The majority of athletes maintained a PBF of 10-20% (n = 87). PBF did not demonstrate a significant correlation between Cr and cystatin C levels, with the PBF 20-30% cohort approaching moderate correlation (R2 = 0.49, p =<0.0001). Conclusions Our study affirms that elite athletes maintain an increased BMI and low PBF. Hence, cystatin C may demonstrate a more accurate reflection of renal function in these patients, as Cr may be inaccurately elevated. Disclosure Any of the authors act as a consultant, employee or shareholder of an industry for: Abbie, American Medical Systems, Augmenta LLC, Clarus Therapeutics, Endo Pharmaceuticals, Lipocine, Vault Health