Study: Gastric bypass ups kidney stone risk

ROCHESTER, Minn., Nov. 13 (UPI) -- Morbidly obese patients who had gastric bypass surgery to lose weight have increased risk factors for kidney stones, says a U.S. study

"Gastric bypass surgery appears to lead to changes in the chemical composition of urine that could favor the formation of kidney stones," said Dr. Rajiv Kumar of Mayo Clinic College of Medicine in Rochester, Minn., one of the study authors.

"Based upon this information, we suggest that patients take appropriate measures to reduce the potential for kidney stone formation."

The study found that a group of patients who had bypass surgery 12 months previously showed several chemical changes that have been linked to an increased risk of kidney stones. These included a significant increase in the level of oxalate, a chemical that increases kidney stone risk by binding to calcium.

Gastric bypass patients may want to talk to their doctors about dietary changes and other steps they can take to reduce their risk of kidney stones, the researchers suggest.

The findings are scheduled to be presented this week at the American Society of Nephrology's 39th Annual Meeting and Scientific Exposition in San Diego.