Sex Differences of Kidney Stone Urine Risk Factors after Roux-en-Y Gastric Bypass.

INTRODUCTION Roux-en-Y gastric bypass (RYGB) is a bariatric surgical procedure that is associated with higher risk of kidney stones after surgery. We examined urine composition in 18 men and women before and after RYGB to examine differences in kidney stone risk. METHODS Three 24-h urine collections were performed before and 1 year after RYGB. We analyzed mean urinary values for pre- and post-RYGB collections and compared men and women. RESULTS Seven men and eleven women completed pre- and post-RYGB urine collections. Pre-RYGB, men had higher calcium oxalate supersaturation (CaOx SS) (7.0 vs. 5.0, p = 0.04) compared with women. Post-RYGB, women had higher urine CaOx SS (13.1 vs. 4.6, p = 0.002), calcium phosphate supersaturation (1.04 vs. 0.59, p = 0.05), and lower urine volumes (1.7 vs. 2.7L, p < 0.001) compared with men. DISCUSSION/CONCLUSION There are important differences in urine composition by sex that may contribute to higher kidney stone risk in women after RYGB compared with men.