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Kidney Week

Abstract: PO0408

Roux-en-Y Gastric Bypass and Kidney Stones

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical


  • Prochaska, Megan, University of Chicago, Chicago, Illinois, United States
  • Chapman, Arlene B., University of Chicago, Chicago, Illinois, United States
  • Coe, Fredric L., University of Chicago, Chicago, Illinois, United States
  • Worcester, Elaine M., University of Chicago, Chicago, Illinois, United States

Roux-en-Y gastric bypass (RYGB) is a bariatric surgical procedure that is highly effective in the management of morbid obesity but also associated with higher risk of kidney stone formation after surgery. It is not known why RYGB is associated with higher kidney stone risk but it may be due to changes in urine composition, such as high urine calcium oxalate supersaturation (CaOx SS) and calcium phosphate supersaturation (CaP SS). It is not known who is at risk for high urine CaOx SS after surgery. We examined 24-hour urine composition in 18 men and women before and after RYGB to look for predictors of urine high CaOx SS and CaP SS.


Patients were recruited from a bariatric surgery clinic prior to scheduled laparoscopic long-limb RYGB. Three consecutive 24-hour urine collections performed in a Clinical Research Center both before and 1 year after surgery. We performed Welch’s 2-sample and paired t-tests to compare mean urinary values for pre- to post-RYGB collections and to compare men to women in the post-RYGB collections. We used linear regression to evaluate predictors of urine CaOx SS and CaP SS.


Seven men and eleven women completed pre- and post-RYGB urine collections. Post-RYGB, women had a significantly higher urine CaOx SS (13.1 vs. 4.6, p=0.002), CaP SS (0.59 vs. 1.04, p=0.05), and lower urine volumes (1.7 vs. 2.7L, p<0.001) compared with men. There were no differences by sex in CaOx SS or urine volume pre-RYGB. Both men and women had high oxalate in the pre- and post-RYGB collections. Urine volume was most strongly associated with urine CaOx SS with a difference in urine CaOx SS of -6.4 (-8.7 to -4.0) for every 1 liter of urine volume excretion. Citrate was also associated with change in -0.01 (-0.01 to -0.002) per mg of citrate. Calcium and oxalate were not significantly associated. For CaP SS, higher urine calcium and pH (1.3, 0.8 to 1.7) were associated with higher CaP SS (Calcium 0.01mg, 0.008 to 0.12mg; pH 1.3, 0.8 to 1.7). Higher urine volume (-0.4 -0.6 to -0.1) was associated with lower CaP SS and citrate was not significant.


There are important differences in urinary parameters by sex that may contribute to differences in kidney stone risk after RYGB. Women may be at higher risk for kidney stone formation after RYGB compared with men.


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