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| |  Gastric Bypass Surgery Linked to Increased Risk of Kidney Stones CHICAGO -- June 26, 2008 -- Morbidly obese patients who undergo a particular type of gastric bypass surgery, Roux-en-Y gastric bypass (RYGB), are at an increased risk of developing kidney stones earlier than previously thought, according to research published in the June issue of the Journal of the American College of Surgeons. "Our data suggest that RYGB is associated with an increased risk of forming kidney stones as early as 3 months postoperation," said lead investigator Manoj Monga, MD, University of Minnesota, Minneapolis, Minnesota. "We hope our findings and subsequent research will eventually allow clinicians to more accurately counsel patients on their individual risk of kidney stones and develop strategies for the prevention of this sometimes painful condition, such as dietary modification and medical therapy." Although RYGB is a safe and effective treatment for morbid obesity, nephrolithiasis has recently raised concerns among patients undergoing RYGB. "Although this study demonstrates that there is a higher risk for developing kidney stones, it is important to weigh the risk against the many benefits that RYGB has for the morbidly obese patient, including decreasing cardiac morbidity and improving diabetes," Dr. Monga added. Surgeons conducted a prospective, longitudinal study of 24 morbidly obese adults (9 men, 15 women) from a university-based bariatric surgery clinic scheduled to undergo RYGB between December 2005 and April 2007. Of the patients, 5 had a history of nephrolithiasis. Patients provided 24-hour urine collections for analysis 7 days before and 90 days after surgery. The primary endpoints were change in the amount of the compound oxalate in the urine and the relative supersaturation of calcium oxalate from baseline to 3 months post-RYGB. Significant increases were noted in urinary oxalate excretion (31 +- 10 mg/d vs 41 +- 18 mg/d, P = .026) and relative supersaturation of calcium oxalate (1.73 +- 0.81 vs 3.47 +- 2.59, P = .030) at only 3 months post-RYGB. Six patients (25%) developed de novo hyperoxaluria, with oxalate excretion increasing from 26 +- 12 mg/d to 63 +-12 mg/d (P = .0046). There were no preoperative patient characteristics predictive of increased risk of kidney stone formation. The reason for increased likelihood of nephrolithiasis following this type of gastric bypass surgery is not entirely understood. A possibility is that the anatomic rearrangement caused by the operation establishes a mildly malabsorptive state, which may be responsible for the increase in the excretion of urinary electrolytes. Kidney stones could also result from an alteration in the gut microflora caused by the procedure.
SOURCE: Weber Shandwick Worldwide
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