Gastric Bypass Surgery Raises Kidney Stone Risk

The Roux-en-Y procedure, the most popular type of gastric bypass surgery, appears almost to double the chance that a patient will develop kidney stones, according to a new study.

Researchers from Johns Hopkins University (JHU) School of Medicine (Baltimore, MD, USA) used a U.S. national insurance claims database to identify 4,639 patients who had undergone Roux-en-Y surgery between 2002 and 2006. The researchers then identified a second set of 4,639 patients who had similar characteristics including age, gender, and body mass index (BMI) who did not undergo surgery. All patients had at least three years of continuous claims data follow-up. Using medical information encoded in the database for both patient populations, the researchers examined which patients either were diagnosed with kidney stones or had treatment for this condition.

The results showed that after Roux-en-Y gastric bypass surgery 7.65% of the patients were diagnosed with urolithiasis, compared to 4.63% of obese patients in the control group. Logistic regression demonstrated that Roux-en-Y gastric bypass surgery was a significant predictor of being diagnosed with a urinary calculus as well as undergoing a surgical procedure; while only 8% of the Roux-en-Y patients developed kidney stones, they were nearly twice as likely to get this condition as the patients with similar characteristics that did not undergo weight loss surgery. The researchers also found that participants in the treatment cohort more commonly underwent shock wave lithotripsy ureteroscopy. The study was published in the June 2009 issue of the Journal of Urology.

"Our study is not an indictment of bariatric surgery; the benefits of this surgery are well known,” said lead author Brian Matlaga, M.D., an assistant professor of urology at JHU. "Rather, we'd like to help physicians understand that their bariatric patients could be at risk for kidney stones, a condition that could be avoidable with proper preventative care.”

Since kidney stones are often caused by an excess of a dietary component known as oxalate (which normally binds with calcium and is flushed out of the body), the researchers speculated that Roux-en-Y surgery might reduce the amount of calcium that the patients absorb, contributing to kidney stone formation. Consequently, the researchers suggest, doctors may be able to help patients avoid kidney stones through calcium supplements or other interventions.

A second study by the same researchers, published in the august 2009 issue of Urology, demonstrated that gastric banding, on the other hand, is not associated with an increased risk for kidney stone disease or kidney stone surgery in the postoperative period.

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Johns Hopkins University School of Medicine