Renal Function 1 Year after Bariatric Surgery: Influence of Roux-en-Y Gastric Bypass and Identification of Pre-Operative Predictors of Improvement

Background While evidence of improved renal function following gastric bypass exists, pre-operative predictors of this improvement are not completely known. Objectives To assess the glomerular filtration rate (GFR) 1 year after Roux-en-Y gastric bypass (RYGB) and to identify pre-operative predictors associated with the improvement of renal function. Methods A historical cohort study, which included 109 obese patients before and 12 months after RYGB, was classified into subgroups according to GFR (normofiltration, hypofiltration (GFR < 5th percentile), and hyperfiltration (GFR > 95th percentile)). The 5th and 95th percentiles were 90 and 120 mL/min/1.73 m 2 , respectively. The primary outcome was the variation of GFR (%GFR) estimated by the Chronic Kidney Disease - Epidemiology Collaboration (CKD-EPI) formula, calculated using serum creatinine, ethnicity, and gender. Results The mean age was 38.3 ± 10.3 years and 77% were female; 52.3% presented hypertension and 27.5% type 2 diabetes. One year after surgery, the mean BMI decreased from 36.7 ± 3.6 to 28.8 ± 3.3 kg/m 2 ( p < 0.001). Pre-surgically, 37.6% presented hypofiltration, 47.7% normofiltration, and 14.7% hyperfiltration. The overall GFR increased from 95.5 ± 19 to 104 ± 16.4 mL/min (10.9%) ( p < 0.001). The overall post-surgical %GFR was negatively correlated with the pre-surgical GFR ( R = − 0.687; p < 0.001). In the hypofiltration and normofiltration subgroups, the post-surgical %GFR was negatively correlated with age ( R = − 0.328, p = 0.036; and R = − 0.355, p = 0.004, respectively) and pre-surgical GFR ( R = − 0.436, p = 0.04; and R = − 0.528, p < 0.001, respectively). Conclusion RYGB led to a significant improvement in renal function, mainly among patients with a worse pre-operative renal function. In the hypofiltration and normofiltration subgroups, a younger age was associated with better outcomes.