WLS Bypass Increases Risk for Kidney Stones

Author Ron Merk
Source – Newswise

We’ve heard this before and the latest study confirms that Weight Loss Surgery patients who undergo gastric bypass surgery have a higher risk of developing kidney stones. The reason is that the bypass surgery results in changes in their urine composition most likely due to the mal-absorption  of various minerals via the bypass of  the small intestine as part of their RnYGB surgery.

A new study, published in the March 2010 issue of The Journal of Urology, from research carried out by UT Southwestern Medical Centre found that some of these urinary changes place weight-loss surgery patients at higher risk for developing kidney stones than obese patients who do not undergo the procedure.

For the study, researchers collected urine samples from 38 study participants. There were 16 women and three men in each of two groups. One group had undergone Roux-en-Y gastric bypass (RnY or RYGB) surgery; the second group contained normal obese individuals. RnYGB, which is one of the most commonly performed weight-loss procedures, involves the creation of a small gastric pouch and the bypass of part of the small intestine.

RnYGB’s high weight loss success is a result of this combination of forcing the patient to only be able to eat small portions due to the stomach “pouch” size and the deliberate mal-absorption component via by-passing a part of the small intestine which reduces the absorption of food  (nutrients, minerals & vitamins) passing through the body.

The study found that the a material called oxalate was significantly greater in the urine of the participants who had the surgical procedure than those who did not (47 percent, compared with 10.5 percent, respectively). In addition, the amount of a chemical called citrate in the urine was low in many gastric bypass patients in comparison to the obese nonsurgical group (32 percent to 5 percent).

Oxalate is found in the majority of kidney stones, while citrate inhibits stone formation.

“Almost half of the patients who had undergone gastric bypass and did not have a history of kidney stones showed high urine oxalate and low urine citrate – factors that lead to kidney-stone formation,” said Dr. Naim Maalouf, assistant professor of internal medicine in the Charles and Jane Pak Center for Mineral Metabolism and Clinical Research and the study’s lead author.

The cause for stone formation after bariatric surgery is not entirely clear, but the study reinforces the message that weight-loss surgery patients and their physicians should be alert to the heightened risk, Dr. Maalouf said.

“These findings illustrate that the majority of patients are at risk for kidney-stone formation after RnYGB,” Dr. Maalouf said. “This complication may not be well-recognized in part because it tends to occur months to years after the bypass surgery.”

Other UT Southwestern researchers involved in the study were Dr. Eve Guth, assistant professor of internal medicine; Dr. Edward Livingston, chief of GI/endocrine surgery; and Dr. Khashayar Sakhaee, chief of mineral metabolism and the study’s senior author.

The research was supported by the National Institutes of Health.

The message here for RnYGB patients is to make sure you inform your doctor of your increased risk of kidney stones and be vigilant for signs and symptoms.  Should you end up in an Emergency Room don’t forget to mention to the ER doctor you’ve had RnYGB and that’s is very common for bypass patients to develop kidney stones. It could save you hours or even days of pain.

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• Do You Know What Causes Kidney Stones? (yearn2blog.com)
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