[Renal function assessment and procedure selection in metabolic and bariatric surgery]

Obesity is an important risk factor for the development and progression of chronic kidney disease (CKD), whereas CKD may increase perioperative risk in patients undergoing metabolic and bariatric surgery. Surgical procedures differ in their effects on acute kidney injury, volume depletion, nephrolithiasis, enteric hyperoxaluria, nutritional status, and immunosuppressant exposure; therefore, kidney function assessment is essential for risk stratification and procedure selection. In patients with obesity, serum creatinine and cystatin C may be affected by muscle mass, adiposity, and inflammation, while body surface area indexing and postoperative changes in body composition may further complicate the interpretation of estimated glomerular filtration rate. Preoperative evaluation should establish whether kidney abnormalities are chronic and should include creatinine-based estimated glomerular filtration rate and the urine albumin-to-creatinine ratio as initial assessments. Measurement of cystatin C, measured glomerular filtration rate, or 24-hour urine analysis may be added when clinically indicated. Procedure selection should integrate CKD stage, albuminuria category, the trajectory of kidney function, previous acute kidney injury, the risk of nephrolithiasis or hyperoxaluria, dialysis and kidney transplantation plans, and the need for metabolic and antireflux efficacy. Sleeve gastrectomy is generally favored in patients with advanced CKD, those receiving dialysis, kidney transplant candidates, and patients at high risk of hyperoxaluria. Roux-en-Y gastric bypass may be considered after multidisciplinary assessment in patients with stable kidney function, low stone risk, and a greater need for metabolic or antireflux effects. Postoperative kidney function should be evaluated in conjunction with changes in body composition, albuminuria, glomerular hyperfiltration, and kidney-related clinical events. This review summarizes kidney function assessment, procedure selection, and postoperative reassessment in patients undergoing metabolic and bariatric surgery.