Bariatric surgery is associated with renal function improvement

Weight loss after bariatric surgery improves both blood pressure and glycemic control following surgery. The effect of bariatric surgery on renal function is not well characterized. In this study, we sought to quantify the change in renal function over time following surgery.

We retrospectively reviewed all patients who underwent laparoscopic Roux-en-Y gastric bypass (LRYGB) or laparoscopic sleeve gastrectomy (LSG) between 2012 and 2014 at our institution. The glomerular filtration rate (GFR, mL/min) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Body mass index (BMI, kg/m²) and percent weight loss (%WL) were calculated following the surgery.

A total of 149 patients who underwent bariatric surgery were included in this study: LRYGB (n = 86 and LSG (n = 63). In LRYGB group, baseline BMI (kg/m², ±SD) and GFR (mL/min, ±SD) were 48.5 ± 6.8 and 94.7 ± 23.8, respectively. In comparison, BMI and GFR were 49.1 ± 11.9 kg/m² and 93.1 ± 28.0 mL/min in the LSG group, respectively. Over the follow-up period (19.89 ± 10.93 months), the patients who underwent LRGYB lost a larger percentage of weight as compared to those in the LSG group (29.9 ± 11.7% vs 22.3 ± 10.7%; p = <0.0001). Overall, GFR improved in both LRYGB (101.0 ± 25.8 mL/min) and LSG groups (97.9 ± 25.8 mL/min) and was not significantly different between the two groups. Of patients with a GFR < 90 mL/min prior to weight loss surgery (n = 62), 42% had improvement of their GFR to > 90 mL/min postoperatively (p < 0.001). There was no relationship between weight loss percentage and GFR improvement (p = 0.8703).

Bariatric surgery was associated with improvement in postoperative renal function at almost two years following surgery but was not different for LRYGB versus LSG. The gain in GFR was independent of percentage of weight lost suggesting an alternate mechanism in the improvement of renal function other than weight loss alone.