Jared M. Whitson*, G. Bennett Stackhouse, Marshall L Stoller, San Francisco, CA.

Introduction and Objective: Obesity is an increasingly prevalent problem in the United States. Obese patients with kidney stones may be particularly difficult to treat. Extracorporeal shock wave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy are more challenging and sometimes require specialized instruments. Obese patients are being treated with bariatric surgery at an ever increasing rate. These operations result in micronutrient malabsorption and drastic dietary changes that are thought to increase stone risk. We examined our patients with hyperoxaluria to detect the impact of bariatric surgery on stone risk profile.

Methods: 24-hour urine collections of all patients referred to our clinic for nephrolithiasis in the past 4 years were reviewed. Those patients with moderate (45-75 mg/day) or severe (>75 mg/day) hyperoxaluria were identified. Retrospective chart review was performed to determine their medical and surgical histories.

Results: Five hundred sixty four patients had evaluable data from 24-hour urine collections. Of this cohort, 176 had moderate and 39 severe hyperoxaluria. 26 of the 39 patients with severe hyperoxaluria had complete information for review. 5 of these 26 patients were found to have a history of bariatric surgery. Those with a history of bariatric surgery had lower urinary calcium (155 vs. 245 mg), citrate (392 vs. 866 mg), pH (6.12 vs. 6.32), uric acid (761 vs 927 mg), and SS CaOx (6.7 vs 11.4) compared to those with severe hyperoxaluria without prior bariatric surgery. The bariatric patients also had a higher urinary ammonium (58 vs 38 mmol), chloride (350 vs. 192 mmol), and sodium (352 vs. 210 mmol) levels. All bariatric surgery patients were taking potassium citrate at the time of the 24 hour urine collection and urinary potassium levels were similar between the two groups (100 vs. 98 mmol).

Conclusions: Bariatric surgery may be a life altering or life saving procedure for morbidly obese patients. Although both groups had similar urinary potassium levels, those with history of bariatric surgery (all taking potassium citrate) had significantly lower urinary citrate values. Despite significantly higher oxalate levels, the bariatric surgery patients had a dramatically lower supersaturation of calcium oxalate, predominantly due to lower urinary calcium excretion. Bariatric surgery results in markedly elevated urinary oxalate levels; yet, their global 24-hour urine parameters may not reflect an increased risk of urinary stone formation.
Wednesday, Wednesday, May 24, 2006 10:00 AM
Moderated Poster: Stone Disease: Research & New Technology (10:00 AM-12:00 PM)

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