TUESDAY, Nov. 10 (HealthDay News) -- Following gastric bypass surgery, patients may develop urinary changes that raise their risk of developing kidney stones, according to research published in the November issue of The Journal of Urology.

Alyssa M. Park, M.D., of the Geisinger Medical Center in Danville, Pa., and colleagues analyzed data from 45 morbidly obese patients, 37 of whom were women, who underwent Roux-en-Y gastric bypass surgery. Subjects -- who were free of a history of stones or inflammatory bowel disease -- underwent 24-hour urine collection and serum assessments preoperatively and again at six to 12 months after the surgery.

The researchers found that urinary oxalate rose significantly, and urinary citrate decreased significantly after the surgery. The authors also note that there was a considerable post-surgical decrease in urinary total volume, urinary uric acid and urinary calcium, and an increase in calcium oxalate supersaturation.

"Several changes were noted in the postoperative 24-hour urine collections that may increase the risk of stone formation. There are several clinical instructions that may be easily performed that could possibly help to counteract this increased risk," the authors write, such as increased fluid intake and decreased fat consumption. "Further investigation should be performed to assess the actual incidence of stone formation in this population as well as the role of these clinical instructions."

The study was supported by Mission Pharmacal, which makes a treatment for kidney stones.

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