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Gastric Bypass May Raise Risk of Kidney Stones

Roux-en-Y surgery appears to increase likelihood of stones as early as three months after surgery

MONDAY, June 30 (HealthDay News) -- Morbidly obese patients who undergo Roux-en-Y gastric bypass are at risk of developing kidney stones as early as three months after surgery, researchers report in the June issue of the Journal of the American College of Surgeons.

Branden G. Duffey, of the University of Minnesota Medical School in Minneapolis, and colleagues conducted a study of 24 morbidly obese adults, including nine men and 15 women, who underwent Roux-en-Y gastric bypass surgery. The patients provided 24-hour urine samples starting seven days before the surgery until 90 days post-surgery.

In six patients (25 percent), urinary oxalate excretion increased from 31 mg/day at baseline to 41 mg/day at three months post-surgery. Over the same period, relative supersaturation of calcium oxalate increased from 1.73 to 3.47 and the patients developed new cases of hyperoxaluria, the researchers report.

"Additional studies are needed to determine the cause of hyperoxaluria after Roux-en-Y gastric bypass, identify patients who might be at increased risk for hyperoxaluria developing, and define specific treatment protocols should hyperoxaluria occur," the authors write. "Additionally, a more comprehensive understanding of the natural course of post-Roux-en-Y gastric bypass hyperoxaluria is needed and will require extended follow-up with evaluation of urinary lithogenic risk factors and incidence of hyperoxaluria-related complications."

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