Measurement of glomerular filtration rate in patients undergoing obesity surgery

BackgroundMost studies on obesity surgery have measured renal function using the estimated GFR. However, due to the reduction of muscle mass, and therefore creatinine that accompanies weight loss, such measures can falsely suggest an improvement in renal function. To balance the risks of surgery versus any potential benefits on renal function, we need to be able to determine renal function using valid and reliable methodologies. In this pilot study we aimed to measure renal function in patients with CKD undergoing obesity surgery using the gold standard Cr-51-EDTA GFR clearance methodology which is independent of measures of muscle mass.MethodsNine consecutive obese patients with CKD underwent obesity surgery. Their renal function was assessed using Cr-51-EDTA GFR, cystatin C and serum creatinine as well as using eGFR equations including MDRD CKD Epi, Cockcroft Gault and CKD Epi cystatin before and 12months after surgery.ResultsRenal function using the Cr-51-EDTA measured GFR did not change significantly after surgery. Similar results were obtained when Cystatin C, CKD Epi cystatin, CKD Epi cystatin creatinine and adjusted Cockcroft Gault Creatinine clearance methods were used. In contrast there were either trends or significant improvements in renal function measured using the MDRD and CKD Epi equations.ConclusionsIn this pilot study using the gold standard Cr-51-EDTA method we found stabilisation in renal function after obesity surgery. Until further definitive data emerge it is critical to balance the risk and benefits of surgery, especially if renal function may not improve as often as previously suggested.