1312 HYPEROXALURIA IS A LONG-TERM CONSEQUENCE OF ROUX-EN-Y GASTRIC BYPASS: A TWO-YEAR PROSPECTIVE LONGITUDINAL STUDY

Abstract

BACKGROUND: Recent studies suggest that patients undergoing Roux-en-Y gastric bypass (RYGB) for morbid obesity are at risk for hyperoxaluria, nephrolithiasis, and oxalate nephropathy. Our objective was to conduct a long-term prospective longitudinal study to establish the incidence, clinical progression, and severity of hyperoxaluria after RYGB. STUDY DESIGN: Patients undergoing RYGB between December 2005 and April 2007 provided 24-hour urine collections for comprehensive stone risk analysis 1 week before and 3 months and 1 and 2 years after surgery. Primary outcomes were changes in 24-hour urinary oxalate excretion and relative supersaturation of calcium oxalate from baseline to 2 years post-RYGB. RESULTS: The cohort consisted of 21 patients, including 5 (24%) men and 16 (76%) women. Mean preoperative age and body mass index (calculated as kg/m 2 ) were 48.2 10.5 years (range 25 to 64 years) and 50.5 9.1 (range 39.7 to 66.6), respectively. Urinary oxalate excretion increased significantly after RYGB (33 9 mg/day versus 63 29 mg/day; p 0.001). De novo hyperoxaluria developed in 11 (52%) patients. Increasing age at the time of surgery was predictive of de novo hyperoxaluria developing (odds ratio 1.162; 95% CI, 1.002–1.347; p 0.046). The percentage of patients with hypocitraturia increased from 10% at baseline to 48% at 2 years. The relative supersaturation of calcium oxalate was unchanged (1.73 0.67 versus 2.20 2.07; p 0.27). CONCLUSIONS: RYGB is associated with a long-term increase in urinary oxalate excretion and decrease in urinarycitrateexcretion.Althoughcalciumoxalaterelativesupersaturationincreasesearlyinthe