Effects of Obesity Surgery on Renal Function

Completed

Brief Summary: 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.

Detailed Description: 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

Recruitment & Eligibility

Inclusion Criteria

Patients with a BMI of >35kg/m2 approved for obesity surgery based on the NICE criteria.
Patients with a GFR <60 mL/min/1.73 m2

Exclusion Criteria

Primary Outcome Measures

Name	Time	Method
Changes in Glomerular Renal Function After Weight Loss Surgery as Measured by 51Cr-EDTA Clearance	12 months	The outcome measure is reported as the number of participants who achieved a change in the glomerular renal function after weight loss surgery as measured by 51Cr-EDTA Clearance. 51Cr-EDTA GFR was ascertained using bolus injection of 1.46-2.66 MBq 51Cr-EDTA, with between 6 and 8 venous blood samples were collected at approximately 15, 30, 60, 90, 120, 180, 240, and 300 min to assess 51Cr-EDTA clearance. 51Cr-EDTA GFR was calculated using the Bi-exponential Fitting Method described in the British Nuclear Medicine Society guidelines. The prepared standard and patient samples were counted for 15 and 60 mins respectively using a Wallac 1470 Wizard Gamma Counter (Perkin Elmer Inc., Waltham, Massachusetts, USA). The measured GFR was scaled to BSA in order to maintain uniformity in comparison to reported eGFR.

Secondary Outcome Measures