title: Urinary evaluation after RYGBP: a lithogenic profile with early postoperative increase in the incidence of urolithiasis.
abstract: BACKGROUND
  The objective of this study was to assess predictors for new-onset stone formers after Roux-en-Y gastric bypass (RYGBP).
  
  
  METHODS
  One hundred and fifty-one obese patients underwent RYGBP and were followed for 1 year. The analysis comprised two study time points: preoperative (T0) and 1 year after surgery (T1). They were analyzed for urinary stones, blood tests, and 24-h urinary evaluation. Nonparametric tests, logistic regression, and multivariate analysis were conducted using SPSS 17.
  
  
  RESULTS
  Median BMI decreased from 44.1 to 27.0 kg/m2 (p < 0.001) in the postoperative period. Urinary oxalate (24 versus 41 mg; p < 0.001) and urinary uric acid (545 versus 645 mg; p < 0.001) increased significantly postoperatively (preoperative versus postoperative, respectively). Urinary volume (1310 versus 930 ml; p < 0.001), pH (6.3 versus 6.2; p = 0.019), citrate (268 versus 170 mg; p < 0.001), calcium (195 versus 105 mg; p < 0.001), and magnesium (130 versus 95 mg; p = 0.004) decreased significantly postoperatively (preoperative versus postoperative, respectively). Stone formers increased from 16 (10.6 %) to 27 (17.8%) patients in the postoperative analysis (p = 0.001). Predictors for new stone formers after RYGBP were postoperative urinary oxalate (p = 0.015) and uric acid (p = 0.044).
  
  
  CONCLUSIONS
  RYGBP determined profound changes in urinary composition which predisposed to a lithogenic profile. The prevalence of urinary lithiasis increased almost 70% in the postoperative period. Postoperative urinary oxalate and uric acid were the only predictors for new stone formers.
authors.affiliation: Department of Surgery, State University of Londrina, Rua Santos 777 apto 1302, 86020041, Londrina, Brazil, valezi@sercomtel.com.br.
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Valezi
authors.forename: Paulo Emilio
authors.initials: PE
authors.lastname: Fuganti
authors.forename: Jorge Mali
authors.initials: JM
authors.lastname: Junior
authors.forename: Vinicius Daher
authors.initials: VD
authors.lastname: Delfino
mesh_terms: D000328:Adult; D001938:Brazil / Q000453:epidemiology; D002129:Calcium Oxalate / Q000652:urine*; D005260:Female; D005500:Follow-Up Studies; D015390:Gastric Bypass / Q000009:adverse effects*; D006801:Humans; D015994:Incidence; D008297:Male; D008657:Metabolic Clearance Rate; D009767:Obesity, Morbid / Q000453:epidemiology / Q000601:surgery* / Q000652:urine; D011184:Postoperative Period; D011237:Predictive Value of Tests; D057234:Preoperative Period; D011446:Prospective Studies; D014527:Uric Acid / Q000652:urine*; D052878:Urolithiasis / Q000453:epidemiology* / Q000209:etiology* / Q000652:urine
chemical_list: D002129:Calcium Oxalate; D014527:Uric Acid