Urinary evaluation after RYGBP: a lithogenic profile with early postoperative increase in the incidence of urolithiasis

Obes Surg. 2013 Oct;23(10):1575-80. doi: 10.1007/s11695-013-0916-0.

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.

MeSH terms

  • Adult
  • Brazil / epidemiology
  • Calcium Oxalate / urine*
  • Female
  • Follow-Up Studies
  • Gastric Bypass / adverse effects*
  • Humans
  • Incidence
  • Male
  • Metabolic Clearance Rate
  • Obesity, Morbid / epidemiology
  • Obesity, Morbid / surgery*
  • Obesity, Morbid / urine
  • Postoperative Period
  • Predictive Value of Tests
  • Preoperative Period
  • Prospective Studies
  • Uric Acid / urine*
  • Urolithiasis / epidemiology*
  • Urolithiasis / etiology*
  • Urolithiasis / urine

Substances

  • Calcium Oxalate
  • Uric Acid