Obesity may concurr to cause kidney disease, thus an accurate evalutation of renal function is important in obese subjects. Unfortunately, in these patients the accuracy of prediction formulas based on serum creatinine (PCr) and anthropometric data is quite low.
The aim of this study was evaluate a new method to predict UCr and then creatinine clearance (CCr) by means of a formula which combines the value of body cell mass (BCM) and Pcr.
Seventy-four patients, 54 women, 19-66 years, severely obese (BW 82.5-210 kg; BMI 35.2-73.4 kg/m2) with normal values of PCr (0.57-1.06 mg/dl) were evaluated. Examined parameters: PCr; serum cystatin C; UCr (urine collection 2 hrs); CCr measured with the standard formula (m-CCr); CCr predicted by CG formula (CG-CCr) and by Salazar&Corcoran formula (S&C-CCr). GFR was predicted using 4 variables MDRD formula (MDRD-GFR) and CKD-EPI formula. BCM was measured using a single frequency impedance analyzer. 24h-UCr and CCr were predicted from the individual values of BCM (BCM-CCr).
24h-UCr was 976-3684 mg, m 1801; BCM was 25-74 kg (m 49.4 kg men, 31.7 kg women). A strict linear correlation was found between 24h-UCr and BCM (r=0.78), closer than between 24h-UCr and BW (r=0.64). The difference between BCM-CCr (165±41 mL/min) and m-CCr (167±44 mL/min) was insignificant. Quite different estimates were given by the other prediction formulas: C&G-CCr (199±72 mL/min), S&C-CCr (149±47mL/min), MDRD-GFR (122±34 mL/min), CKD-EPI-GFR (131±32 mL/min). BCM-CCr values showed also a good correlation with m-CCr (r=0.767, p<0.0001) and the concordance between the two measures resulted similar for all explored values of renal function.
Urinary creatinine excretion and creatinine clearance can be more accurately predicted in severely obese patients from the measurement of body cell mass combined with serum creatinine, than with other formulas.
