Neil Osterweil

May 17, 2014

ORLANDO, Florida — Better control of glycemia in type 2 diabetes may reduce the risk of developing kidney stones, according to the results of a new retrospective study.

"The better you control your diabetes, the lower your risk of forming a stone," said Manoj Monga, MD, ‎director of the Center for Endourology and Stone Disease at the Cleveland Clinic.

"Some of this is related to preventing the low urine pH that allows crystals to form, but there also may be some direct effect of insulin that we currently don't understand," said Dr. Monga.

Dr. Monga spoke at a briefing here at the American Urological Association 2014 Annual Scientific Meeting.

Both diabetes and kidney stones are common in the United States, each affecting an estimated 26 million people, or 8.3% of the population. In addition, there is considerable overlap, with approximately 21% of patients with type 2 diabetes developing kidney stones, said Dr. Monga.

Part of the reason for this predisposition to nephrolithiasis is that people with diabetes have impaired ammonia genesis and higher acid excretion due to lower urine pH than the population without diabetes.

A Retrospective Study

To see whether diabetic medications could protect patients against low urinary pH and thereby reduce the risk for stones, Dr. Monga and colleagues took a retrospective stroll through the Cleveland Clinic database. They identified 1831 patients with type 2 diabetes and kidney stones treated from July 2002 through January 2013. Of this group, 375 (20.5%) used insulin and 1456 (79.5%) took an oral antidiabetic drug.

In a linear regression analysis that controlled for age, sex, body mass index, glycosylated hemoglobin (HbA1c) levels, and urine pH, insulin therapy was significantly protective against low urine pH (P = .001), whereas HbA1c levels were associated with more acidic urine (P < .001).

Each percentage point increase in HbA1c was associated with a decrease in urine pH of .066 (P < .001).

Using a pH cutoff of 5.5 or less, the authors found that 45.6% of patients who used insulin had low urine pH, compared with 57.4% of those who took oral medications (P < .001).

A subanalysis by type of oral antidiabetic drug found no difference between thiazolidinediones (rosiglitazone, pioglitazone, etc) and other oral agents.

There were no significant differences in other 24-hour urine stone risk parameters or in the composition of stones between the groups.

Dr. Monga said that the results are supported by a separate study his group conducted using data from the National Health and Nutrition Survey Examination, which showed that people who were active recreationally had a lower risk for stones. Exercise, along with diet, is a key component of HbA1c control.

"I think we're really just at the beginning of understanding the relationship between diabetes and stone disease," said Margaret Pearle, MD, PhD, professor of urology at the University of Texas Southwestern Medical Center at Dallas and the Center for Mineral Metabolism and Clinical Research, who was not involved in the study.

"We understand the link with uric acid stones, but I think we have less of an understanding of the link to calcium stones," Dr. Pearle said in an interview with Medscape Medical News.

"It may be that the low urine pH is also a subsequent risk for calcium stones, but whether or not there's a more direct link between diabetes and calcium stones, I'm not sure. I think that needs to be further explored."

Dr. Pearle noted that diabetes is just one of several risk factors contributing to the increased incidence of kidney stones, including obesity and increased consumption of animal proteins.

The study was internally funded. Dr. Monga and Dr. Pearle reported no relevant financial relationships.

American Urological Association (AUA) 2014 Annual Scientific Meeting. Abstract MP27-20. Presented in a briefing May 17 and in a moderated poster session May 18, 2014.

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