title: Calcium oxalate supersaturation increases early after Roux-en-Y gastric bypass.
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.
authors: Division of Nephrology and Hypertension, Fletcher Allen Health Care, Burlington, Vermont. Electronic address: varunagrawal1996@yahoo.com.
authors: Varun
authors: V
authors: Agrawal
authors: Department of Medicine, Baystate Medical Center, Springfield, Massachusetts and Tufts University School of Medicine, Boston, Massachusetts.
authors: Xiao J
authors: XJ
authors: Liu
authors: Department of Pediatrics, Baystate Medical Center, Springfield, Massachusetts and Tufts University School of Medicine, Boston, Massachusetts.
authors: Thomas
authors: T
authors: Campfield
authors: Department of Surgery, Baystate Medical Center, Springfield, Massachusetts and Tufts University School of Medicine, Boston, Massachusetts.
authors: John
authors: J
authors: Romanelli
authors: Division of Endocrinology, Baystate Medical Center, Springfield, Massachusetts and Tufts University School of Medicine, Boston, Massachusetts.
authors: J
authors: J
authors: Enrique Silva
authors: Renal Division, Baystate Medical Center, Springfield, Massachusetts and Tufts University School of Medicine, Boston, Massachusetts.
authors: Gregory L
authors: GL
authors: Braden
mesh_terms: D000328:Adult; D002129:Calcium Oxalate / Q000652:urine*; D005260:Female; D015390:Gastric Bypass / Q000009:adverse effects*; D006801:Humans; D006959:Hyperoxaluria / Q000209:etiology; D007669:Kidney Calculi / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000601:surgery* / Q000652:urine; D011446:Prospective Studies
chemical_list: D002129:Calcium Oxalate
keywords: Calcium oxalate; Gastric bypass surgery; Hyperoxaluria; Obesity; Supersaturation