Renal function and body composition before and after intestinal bypass operation in obese patients

Abstract

The distribution volume of [⁵¹Cr]EDTA, as an estimate of the extra cellular fluid volume (ECV), glomerular filtration rate (GFR) and urinary excretion rate of endogenous creatinine (u_c), as an index of muscle mass, were determined in obese patients before and after intestinal bypass operations. The results were compared to those in non-obese controls with the same age and height. GFR, ECV and U_c were all significantly increased to the same extent (about 40%) in thirteen patients examined before operation (overweight 86–159%). Means of the ratio GFR/ECV and standard GFR (i.e. GFR corrected to a body surface area of 1.73 m²) did not differ from those in the controls. In eight patients examined before and 1 year after operation (body weight reduction 23–79 kg), GFR, ECV and u_c decreased in all, whereas the ratio GFR/ECV and standard GFR were unchanged and remained normal. ECV was significantly increased by 20% in nineteen patients investigated 1–7 years after operation (mean overweight 42%) whereas the mean of u_c did not differ from that in the controls. Using the ratio GFR/ECV as reference for the function of the kidneys, the present study shows that the renal function in otherwise healthy obese subjects is normal throughout the whole range of overweight, and that standard GFR is a reliable parameter to assess the renal function even in patients with extreme obesity. The body weight reduction following intestinal bypass operation is in part due to a fall in muscle mass, but the results suggest that a normal relation between body cell mass and body water is not achieved.

Key Words:

• body composition
• extra cellular fluid volume
• glomerular filtration rate
• jejunoileostomy
• obesity
• renal function