Stone formation and management after bariatric surgery.

Obesity is a significant health concern and is associated with an increased risk of nephrolithiasis, particularly in women. The underlying pathophysiology of stone formation in obese patients is thought to be related to insulin resistance, dietary factors, and a lithogenic urinary profile. Uric acid stones and calcium oxalate stones are common in these patients. Use of surgical procedures for obesity (bariatric surgery) has risen over the past two decades. Although such procedures effectively manage obesity-dependent comorbidities, several large, controlled studies have revealed that modern bariatric surgeries increase the risk of nephrolithiasis by approximately twofold. In patients who have undergone bariatric surgery, fat malabsorption leads to hyperabsorption of oxalate, which is exacerbated by an increased permeability of the gut to oxalate. Patients who have undergone bariatric surgery show characteristic 24 h urine parameters including low urine volume, low urinary pH, hypocitraturia, hyperoxaluria and hyperuricosuria. Prevention of stones with dietary limitation of oxalate and sodium and a high intake of fluids is critical, and calcium supplementation with calcium citrate is typically required. Potassium citrate is valuable for treating the common metabolic derangements as it raises urinary pH, enhances the activity of stone inhibitors, reduces the supersaturation of calcium oxalate, and corrects hypokalaemia. Both pyridoxine and probiotics have been shown in small studies to reduce hyperoxaluria, but further study is necessary to clarify their effects on stone morbidity in the bariatric surgery population.