Effects of Obesity Surgery on Renal Function

• Microalbuminuria, creatinine clearance, Cystatin C. [ Time Frame: 12 months ] [ Designated as safety issue: Yes ]
  Compare different ways of measuring renal function after weight loss surgery.
• Differences in alterations in renal function dependent on the used surgical procedure. [ Time Frame: 12 months ] [ Designated as safety issue: Yes ]
  Compare the renal function among the three different surgical cohorts, namely gastric bypass, gastric band, and sleeve gastrectomy.

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

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 m2

• Obesity Related Glomerulopathy
• Impaired Renal Function
• Bariatric Surgery

• gastric band
  Patients having gastric band will have blood and urine tests, and 51 Cr-EDTA clearance to assess renal function. These are taken before and after the surgery at 6 weeks , 6 months and 12 months.
• sleeve gastrectomy
  Patients having sleeve gastrectomy will have blood and urine tests, and 51 Cr-EDTA clearance to assess renal function. These are taken before and after the surgery at 6 weeks , 6 months and 12 months.
• gastric bypass
  Patients having gastric bypass will have blood and urine tests, and 51 Cr-EDTA clearance to assess renal function. These are taken before and after the surgery at 6 weeks , 6 months and 12 months.

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:

• Allergy to chromium