Effects of Obesity Surgery on Renal Function

Increasing risk of impaired renal function as a result of obesity is well known. Early data has postulated that weight loss might improve kidney function, but the evidence is rather limited due to the difficulties in measuring glomerular filtration rate(GFR) after weight loss. Cystatin C, GFR measurement using Cockcroft-Gault (CCG) and Modification of Diet in Renal Disease (MDRD) equations, have all yield conflicting results after weight loss surgery. The study aim to assess: 1. use of 51Cr-EDTA Clearance as the methodological gold standard in evaluating changes in renal function before and after weight loss surgery. 2. the reliability of using MDRD, CCG and Cystatin C in measuring GFR after weight loss surgery 3. the differences in alterations in renal function dependent on the surgical procedures( gastric bypass, gastric band, sleeve gastrectomy). 4. the use of urine albumin/creatinine ratio in detecting alterations in microalbuminuria.

This is a prospective study on obese human subjects undergoing bariatric surgery. Forty-five patients due to undergo gastric bypass (n=15), gastric banding (n=15), and gastric sleeve surgery (n=15) will be recruited. Subjects will be screened prior to entry into the study with full history, examination, routine bloods (FBC, U+E, liver function tests, and glucose). 1. Blood samples and 24h urine specimens are taken at four time points: preoperatively as well 6 weeks, 6 and 12 months postoperatively. 2. The following methods of GFR assessment will be executed the same time point: measurement of serum creatinine concentration, calculation of the abbreviated and extended MDRD formulae, CCG, creatinine clearance, serum Cystatin C concentration and the 51Chromium-EDTA clearance. Inclusion criteria 1. Patients with a BMI of \>35kg/m2 approved for obesity surgery based on the NICE criteria. 2. Patients with a GFR \<60 mL/min/1.73 Exclusion criteria 1\. Allergy to chromium