title: Urolithiasis risk factors in the bariatric population undergoing gastric bypass surgery.
abstract: BACKGROUND
  Previous studies have suggested an increased risk of forming symptomatic urolithiasis after Roux-en-Y gastric bypass (RYGB) attributed to the development of hyperoxaluria. The objective of our investigation was to evaluate changes in the urine milieu after RYGB that might explain the increased risk of urolithiasis.
  
  
  METHODS
  Patients underwent serum and urine chemistry tests 1 week before and 6 months after RYGB at a university hospital. The postoperative urolithiasis risk factors were compared with the preoperative values. Statistical analysis was performed using paired t tests. Significant changes were identified as P ≤ .05.
  
  
  RESULTS
  A total of 38 patients (7 men and 31 women) submitted samples both before and after RYGB. The mean patient weight had decreased from 131 kg to 92 kg. The mean serum creatinine decreased from .83 to .72 mg/dL (P = .0004). Urinary changes known to increase the risk of urolithiasis include a decrease in volume (2-1.5 L/d, P = .03), an increase in calcium (139-182 mg/d, P = .04), and an increase in oxalate (38-48 mg/d, P < .001). The urinary supersaturation indexes for calcium oxalate (4.9-10.5, P < .001) increased.
  
  
  CONCLUSIONS
  Our results confirm that patients undergoing RYGB develop changes in the urinary milieu predisposing them to forming urinary stones. Urolithiasis risk is multifactorial and is related to more than just hyperoxaluria. A patient's long-term risk of developing stones and the effect on renal function is unknown. Preoperative counseling of patients regarding their risk of forming stones and dietary counseling to minimize their risk of developing stones postoperatively is warranted.
authors.affiliation: Department of Urology, University of California Davis Medical Center, Sacramento, California 95817, USA. jennifer.wu@ucdmc.ucdavis.edu
authors.forename: Jennifer N
authors.initials: JN
authors.lastname: Wu
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Craig
authors.forename: Karim
authors.initials: K
authors.lastname: Chamie
authors.forename: John
authors.initials: J
authors.lastname: Asplin
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Ali
authors.forename: Roger K
authors.initials: RK
authors.lastname: Low
mesh_terms: D000328:Adult; D005260:Female; D015390:Gastric Bypass / Q000009:adverse effects*; D006801:Humans; D006959:Hyperoxaluria / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000601:surgery; D011446:Prospective Studies; D012307:Risk Factors; D052878:Urolithiasis / Q000209:etiology*; D015431:Weight Loss; D055815:Young Adult