Impact of Bariatric Surgery on Metabolic and Lithogenic Risk Factors in Patients with Morbid Obesity

Background: Obesity and metabolic syndrome are risk factors for kidney stones. Bariatric surgeries, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), are options for the management of obesity. Despite the many positive metabolic outcomes, RYGB is also associated with higher risk of kidney stones after surgery. The aim of this study is to determine the modification of lithiasis risk factors in obese patients post-bariatric surgery. Methods: Descriptive, observational and prospective study analyzing lithogenic factors before and 6 months after bariatric surgery. Wilcoxon signed-rank test was used to assess median differences. Ethical approval was obtained Results: 25 patients (24 womens), mean age was 43.3 (±10.6) years. RYGB was performed in 16 and SG in 9. The initial BMI was 47 kg/m 2 (38.0 - 70.4 kg/m2). The post BMI was 30.6 kg/m2 (22 - 50 kg/m2). In the pre-bariatric study, 10 patients had oxaluria higher than 40 mg/day, with a mean of 37.1 ± 17.5 mg/day, 7 had calciuria higher than 250 mg/day, with a mean of 195.7 ± 148.9 mg/day, 15 had uricosuria higher than 600mg/day, with a mean of 706.9 ± 290.7 mg/day, 10 had citraturia less than 300mg/day, with a mean of 514.8 ± 408.5 mg/day, and 10 had magnesiuria less than 73mg/day with a mean of 88.7 ± 46.2 mg/day. 15 had parathyroid hormone (PTH) levels higher than 68pg/mL, with a mean of 83.8 ± 38.4 pg/mL with normocalcemia, 11/15 with hypovitaminosis D. Postoperatively, significant reductions were seen in hyperuricosuria present in 6/25 patients, with a mean of 498.9 ± 194.2 mg/day, p: 0.005, and hypomagnesuria present in 5/25, with a mean of 120.8 ± 68.8 mg/day, p: 0.021. Mean oxaluria was 33.9 ± 25.6mg/day, decreasing in 6/10 patients with preoperative hyperoxaluria and new onset in 3 patients, with no differences based on the type of surgery. Citraturia and calciuria showed a non-significant decrease. Among the 15 patients with elevated (PTH) levels preoperatively, only 6 remained elevated postoperatively, 4 with persistent hypovitaminosis D. Additionally, 3 patients developed postoperative hyperparathyroidism. Conclusion: Morbid obesity presents significant lithogenic risk factors. Bariatric surgery modifies these factors, particularly reducing hyperuricosuria and increasing hypomagnesiuria Funding: Government Support – Non-U.S.