The Excretory Activity of the Kidneys in Children Treated for Overweight or Obesity

Background: Children with excess weight usually exhibit enhanced kidney perfusion resulting in glomerular hyperfiltration. Unfortunately, there are no noninvasive methods to precisely evaluate GFR in children. A useful method of GFR estimation in obese children is the calculation of eGFR according to the Bouvet formula. The aim of the study was to evaluate the influence of excess weight and successful weight reduction on the excretory activity of the kidneys in overweight or obese children. Methods: Creatinine (Cr) and cystatin C (cyC) concentrations were determined and eGFR was calculated using the Bouvet formula in a group of 95 children (9‐13y.), of whom 62 were overweight and 33 obese.The results were compared to the values, which could be found in the population of Polish children (PC) with BMI at the 50th percentile (BMI 17.5±0,8kg/m2, Cr 0.6±0.2mg/dL, cyC 0.54±0.1 mg/L, eGFR 53.1±4.3ml/min). The results obtained before and after a 6‐month weight reduction period in 23 patients, who demonstrated BMI reduction of over 5% were also analyzed. Results: Children with excess weight had higher cyC and eGFR compared to PC. Despite of the different BMI (30±4 vs 24.5±2kg/m2), CyC and eGFR were only slightly higher in obese compared to overweight children (1.21±0.5 vs 1.14±0.4 mg/L ‐ ns and 100.7±29.7 vs 90.8±25 ml/min, p=0.08). In contrast to overweight, in obese children, after a 6‐month weight reduction program, the decreases in cystatin C level (1.3±0.8 vs 0.8±0.4 mg/l, p<0.02) and eGFR (107.6±46.5 vs 79.3±29.2 ml/min, p<0.01) were significant. Further calculations revealed that the decrease in cystatin C level (p<0.04) and eGFR (p<0.04) was only significant in male obese patients. Conclusions: 1. Excess weight in children causes glomerular hyperfiltration. 2. Due to reduced glomerular hyperfiltration, weight loss has a beneficial effect on the excretory activity of the kidneys, in obese children. 3. Following weight reduction, a significant decrease in cystatin C level and eGFR value occurs but only in obese boys.