The effect of restrictive bariatric surgery on urinary stone risk factors

Malabsorptive bariatric procedures such as Roux-en-Y gastric bypass (RYGB) place patients at risk for developing kidney stones. Stone risk factors after purely restrictive procedures such as gastric banding and sleeve gastrectomy are not well characterized. Therefore, we performed a study to examine urinary risk factors of patients who underwent restrictive gastric surgery for bariatric indications.

A total of 18 patients were enrolled in the study; 14 underwent gastric banding and 4 underwent sleeve gastrectomy. All subjects collected 24-hour urine specimens; at least 6 months had elapsed between surgery and urine collection. Standard stone risk parameters were assessed, and comparisons were made with a group of normal adult nonstone-formers, routine stone-formers, and RYGB bariatric surgery subjects.

Urinary oxalate excretion of the restrictive cohort was significantly less than the RYGB cohort (35.4 vs. 60.7 mg/d; P <.001) and not significantly different from that of the normal subjects (32.9 mg/d; P = .798) and routine stone-formers (37.2 mg/d; P = .997). There were no other significant differences in urinary parameters.

Restrictive bariatric surgery does not appear to be associated with an increased risk for kidney stone disease. In particular, urinary oxalate levels were significantly less than those of RYGB subjects and not significantly different from routine stone-formers and nonstone-forming controls.