Impact of bariatric surgery on glomerular filtration rate and metabolic and lithogenic risk factors

Sofía San Román, Unidad Académica de Nefrología, Hospital de Clínicas, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
Lucía Fernández, Unidad Académica de Nefrología, Hospital de Clínicas, Facultad de Medicina, Universidad de la República, Montevideo; Programa de Obesidad y Cirugía Bariátrica, Clínica Médica 3, Hospital Maciel, Facultad de Medicina, UdelaR; Uruguay
Gabriela Ottati, Unidad Académica de Nefrología, Hospital de Clínicas, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
Pilar Portas, Programa de Obesidad y Cirugía Bariátrica, Clínica Médica 3, Hospital Maciel, Facultad de Medicina, UdelaR, Uruguay
Estela Bidegain, Laboratorio de Análisis Clínicos, Hospital Maciel, Montevideo, Uruguay
Mariela Garau, Departamento de Métodos Cuantitativos, Facultad de Medicina, Udelar, Uruguay
Óscar Noboa, Unidad Académica de Nefrología, Hospital de Clínicas, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
Gustavo Bruno, Programa de Obesidad y Cirugía Bariátrica, Clínica Médica 3, Hospital Maciel, Facultad de Medicina, UdelaR, Uruguay

Objective: The aim of this study is to determine the impact of bariatric surgery on glomerular filtration rate (GFR) and lithogenic risk factors. Material and methods: Prospective study conducted at Hospital Maciel (2019–2022). Twenty-five patients undergoing Roux-en-Y gastric bypass or sleeve gastrectomy were included. Clinical, biochemical, and lithogenic parameters were analyzed before and after surgery. Ethical approval was obtained. Results: a total of 25 patients, 24 were women, mean age was 43.3 (± 10.6) years. RYGB was performed in 16/25 and SG in 9/25. Mean BMI decreased by 16.3 kg/m². Diabetes mellitus remitted in 100% and hypertension in 20%. Measured creatinine clearance decreased by 15 ml/min on average (mean postoperative GFR: 118 ml/min). Urinary calcium, uric acid, oxalate, citrate, ammonium, and creatinine excretion decreased, while natriuria and magnesuria increased. No significant proteinuria was detected. Conclusions: Bariatric surgery reduced glomerular hyperfiltration and improved the lithogenic profile, with no major differences between surgical techniques. These findings support the renal benefits of bariatric surgery and the importance of long-term follow-up.

Keywords: Obesity. Glomerular hyperfiltration. Nephrolithiasis. Bariatric surgery.