Abstract
Background
Calcium oxalate (CaOx) nephrolithiasis is an adverse effect of Roux-en-Y gastric bypass
surgery (RYGB). It is unknown when the increased risk for CaOx stone formation occurs
after surgery.
Methods
We studied 13 morbidly obese adults undergoing RYGB with 24-hour urine collections
at 4 weeks before and 1, 2, 4, and 6 months after surgery and computed CaOx relative
saturation ratio (RSR) by EQUIL2.
Results
Eleven patients were female, mean±standard deviation age was 41.1±7.2 years, and none
had diabetes or chronic kidney disease. Median (interquartile range) urinary oxalate
excretion increased linearly from 12.6 (10.9–37.9) mg/24 hr at baseline to 28.4 (14.4–44.0)
mg/24 hr at 6 months (slope = .188; P = .005). CaOx RSR increased significantly at 2 months after RYGB (1.4 [1.2–2.4] to
4.9 [1.7–10.0]; P = .017) and rose throughout the study to 5.7 (3.7–12.2) at 6 months (P = .001) with a positive linear slope (.255; P = .001). One patient had critical CaOx supersaturation (RSR = 34.7) and severe hyperoxaluria
(101.7 mg/24 hr) at 6 months after RYGB. Significant decreases over time were seen
in urine volume and sodium and potassium excretion, but no changes were noted in urinary
pH, calcium, magnesium, or citrate.
Conclusions
Our data suggest that CaOx RSR, and thus risk for nephrolithiasis, rises as early
as 2 months after RYGB and increases gradually in the first 6 months, largely because
of reduced urine volume and increased urinary oxalate excretion. Interventions to
reduce CaOx RSR, such as adequate fluid intake and agents to bind enteric oxalate,
need to be evaluated in patients at risk for nephrolithiasis after RYGB.
Keywords
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Article info
Publication history
Published online: April 29, 2013
Accepted:
March 23,
2013
Received:
February 2,
2013
Footnotes
☆This study was supported by the Baystate Incubator Fund.
☆☆Part of this study was presented at the American Society of Nephrology Renal Week 2010, November 16–21, Denver, Colorado, and the abstract was published in the Journal of the American Society of Nephrology, Volume 21, November 2010, abstract 143.
Identification
Copyright
© 2014 American Society for Metabolic and Bariatric Surgery. Published by Elsevier Inc. All rights reserved.
