Influence of muscle mass and physical activity on serum and urinary creatinine and serum cystatin C

• Grant number: 08/03945-8
• Support Opportunities: Regular Research Grants - Publications - Scientific article
• Start date: June 01, 2008
• End date: November 30, 2008
• Field of knowledge: Health Sciences - Medicine - Medical Clinics
• Principal Investigator: Ita Pfeferman Heilberg
• Grantee: Ita Pfeferman Heilberg
• Host Institution: Departamento de Medicina. Escola Paulista de Medicina (EPM). Universidade Federal de São Paulo (UNIFESP). Campus São Paulo. São Paulo , SP, Brazil

Abstract

In order to address the influence of muscle mass on the estimates and measurements of glomerular filtration rates (GFR), we assessed body composition through bioelectrical impedance in 170 healthy adult individuals (92F/78M) classified by their physical activity as sedentary, mild or moderate/intense. Blood and 24-hour urine samples were obtained for creatinine clearance (CrCl), Cockcroft-Gault (CG) and MDRD equations were calculated with serum cystatin also being determined. Serum and urinary Cr correlated significantly with body weight (r=0.51 95%CI [0.39; 0.61] and r=0.54 95%CI [0.42; 0.64], p<0.05), but the level of correlation with fat-free mass (FFM) was even greater (r=0.73 95%CI [0.66;0.80] and r=0.71 95%CI [0.62; 0.77],p<0.05). Individuals with moderate/intense physical activity presented a higher FFM (55.3±10.0 vs 48.5±10.4 %, p<0.05) and serum Cr (1.04±0.12 vs 0.95±0.17 md/dL, p<0.05) than those classified as sedentary. Serum cystatin did not differ between groups. MDRD was lower than CrCl in the mild physical activity (80±12 vs 87±18 ml/min/24h/1.73m2, p<0.05) and in the moderate/intense physical activity groups (82±13 vs 91±22 ml/min/24h/1.73m2, p<0.05). Conversely, CG was higher than CrCl (93±17 vs 88±17 ml/min/24h/1.73m2, p<0.05) in the sedentary individuals. Intraclass correlation coefficients demonstrated a poor correlation between creatinine clearance and CG (r=0.24) and between creatinine clearance and MDRD (r=0.29). We concluded that formulas used to estimate GFR present an important bias against measured creatinine clearance in healthy individuals with moderate/intense physical activity due to a higher creatinine production from bigger muscle mass. The use of cystatin may be a better alternative to assess renal function in this condition. (AU)