title: Hyperoxaluria is a long-term consequence of Roux-en-Y Gastric bypass: a 2-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.
  
  
  METHODS
  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 <or= 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 urinary citrate excretion. Although calcium oxalate relative supersaturation increases early in the postoperative period, this returns to baseline with long-term follow-up. These data suggest that patients who have undergone RYGB are at risk for oxalate nephropathy developing.
authors.affiliation: Department of Urologic Surgery, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Branden G
authors.initials: BG
authors.lastname: Duffey
authors.forename: Shaheen
authors.initials: S
authors.lastname: Alanee
authors.forename: Renato N
authors.initials: RN
authors.lastname: Pedro
authors.forename: Bryan
authors.initials: B
authors.lastname: Hinck
authors.forename: Carly
authors.initials: C
authors.lastname: Kriedberg
authors.forename: Sayeed
authors.initials: S
authors.lastname: Ikramuddin
authors.forename: Todd
authors.initials: T
authors.lastname: Kellogg
authors.forename: Michelle
authors.initials: M
authors.lastname: Stessman
authors.forename: Angela
authors.initials: A
authors.lastname: Moeding
authors.forename: Manoj
authors.initials: M
authors.lastname: Monga
mesh_terms: D000328:Adult; D000367:Age Factors; D005260:Female; D015390:Gastric Bypass / Q000009:adverse effects*; D006801:Humans; D006959:Hyperoxaluria / Q000209:etiology* / Q000652:urine; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000601:surgery*; D011446:Prospective Studies; D012307:Risk Factors; D018709:Statistics, Nonparametric