Effects of Obesity Surgery on Renal Function

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