The effect of bariatric surgery on renal function.

BACKGROUND: Obesity is associated with albuminuria and impaired renal function. We previously reported on 38 nondiabetics with improved albuminuria after Roux-en-Y gastric bypass (RYGB).

METHODS: Our objectives were to evaluate changes in renal function, urinary albumin-to-creatinine ratio (UACR), and glomerular filtration rate (GFR) in a larger cohort of patients with normal or mildly impaired renal function, undergoing RYGB or sleeve gastrectomy at 1 year postop. This was a retrospective study. Inclusions: patients with preoperative and 1 year postoperative serum and urine albumin and creatinine and weight (kg).

EXCLUSIONS: preop chronic kidney disease (CKD)≥Stage 3 or macroalbuminuria (UACR≥300 mg/g).

PRIMARY OUTCOMES: changes in UACR and estimated GFR (eGFR) at 1 year. The setting was in a public hospital in New York City, 2004-2011.

RESULTS: 158 patients met inclusion criteria; 91.8% female; mean age 40.8 years; 84.2% white Hispanic, 14.6 % black. Hypertension was present in 43.0%, diabetes mellitus in 28.5%. UACR was 21.5±3.2 mg/g, decreasing to 10.2±1.2 mg/g at 1 year (P<.0001). Microalbuminuria was present in 22/158 patients (14%) preop, resolving in 82% at 1 year; pre- versus 1 year postop eGFR, 97.5±2.2 versus 87.1±2.0 mL/min (P<.0001). Hyperfiltration was present in 8.2% preop, decreasing to 4.4% 1 year postop.

CONCLUSION: In this mainly female minority population, UACR decreased within the normal range, while eGFR decreased from normal to the range for Stage 2 CKD at 1 year postop. Microalbuminuria resolved in most affected and hyperfiltration resolved in nearly half of those affected. This study is limited by its retrospective nature. Prospective studies should be performed.