Background: Many studies have shown that hyperfiltration induced by obesity decreases after bariatric surgery, while others also showed an increase in glomerular filtration rate (GFR). Furthermore, the factors that influence GFR after bariatric surgery have been poorly studied. The objective was to study the impact of bariatric surgery on renal function and clarify the factors that determine the evolution of GFR after surgery.
Methods: We prospectively evaluated GFR (assessed with 24-h urinary clearance of creatinine) in all patients who underwent bariatric surgery between 2004 and 2014, before and 1 year after surgery. The links between GFR changes and usual clinical and biological parameters were studied.
Results: Three hundred twenty-three patients with complete urine datasets were included (age 43 ± 11 year, M/F 49/274, BMI 46 ± 7 kg/m2). Excess weight loss was 61 ± 24 % and body surface area (BSA) decreased from 2.26 ± 0.23 to 1.98 ± 0.21 m2 (p < 0.001). Mean GFR decreased from 133 ± 37 to 122 ± 49 ml/min (p < 0.001), in parallel to weight loss. However, GFR decreased in subjects with a preoperative GFR >120 ml/min (p < 0.001), was stable in those with 90 < GFR < 120 ml/min, and increased in those with GFR <90 ml/min (p < 0.01). In multivariate analysis, postoperative GFR did not correlate with metabolic parameters but correlated positively with BSA (p < 0.001) and protein intake (p < 0.01) and negatively with age (p < 0.001) and persistence of antihypertensive drugs (p < 0.001) after surgery.
Conclusion: GFR decreased after bariatric surgery in subjects with hyperfiltration, but increased in subjects with renal failure. Changes in body mass, protein intake, and blood pressure appeared to be the main determinants of GFR evolution after surgery.
Keywords: Bariatric surgery; Creatinine clearance; Glomerular filtration rate; Obesity; Weight loss.