Climate change, stones link will tax health resources

Dallas-A study from the University of Texas Southwestern Medical Center and the University of Dallas, TX, suggests that rising temperatures associated with global warming may be accompanied by a significant, costly increase in the incidence of kidney stones. The research team estimates that by 2050, the projected temperature rise will broaden the so-called "stone belt" to encompass half the population of the United States, increase the annual rate of stones to between 1.6 million and 2.2 million, and push the associated healthcare costs to nearly $1 billion annually. Climate change may increase stone incidence rates by up to 30% in some regions.

While the study attracted substantial attention from the lay media when it was presented at the 2008 AUA annual meeting in Orlando, FL, it appears that the lay press may have overlooked a second study from Toulouse, France. That study suggested that the mechanisms underlying stone creation may respond to rising temperatures over a time span as short as 2 months and that simple hydration may not have as great an effect on those mechanisms as was previously thought.

Margaret S. Pearle, MD, PhD, professor of urology and internal medicine at UT Southwestern, presented the study. She later told Urology Times that she was surprised by the attention the presentation drew.

The Texas team used a data set from the Urologic Diseases in America Project, which contained information from the Veterans Administration on office visits for urolithiasis, and another data set from the Second Cancer Prevention Study on stones, with prevalence stratified by geographic area. A formula based on the VA data indicates a linear 4% increase in stones for every degree centigrade increase in mean annual temperature. The second data set is associated with a threshold temperature above which stone risk increases and a second temperature threshold above which risk slightly decreases.

"We tend to favor the linear model because it appears to more accurately reflect what we see. That is, even is areas where the mean annual temperature exceeds the upper temperature threshold, we continue see an increase in stone risk with rising temperature," Dr. Pearle told Urology Times.

About 40% of the population now lives in the "stone belt," which comprises primarily the southeastern part of the United States. According to the linear model, this belt will broaden by 2050 to include the entire southeastern half of the United States and all of California. By the end of this century, the belt could reach into Pennsylvania, New York, and portions of Washington and Oregon on the west coast, encompassing as much as 66% of the United States population.

"Perhaps the important question raised by this study is, how are we going to prepare for this increase in stone disease with regard to healthcare resources? In some areas there may be as much as a 30% increase in the stone rate. That could have a big impact on health care utilization. Patients with stones usually come to medical attention on an urgent basis, so this raises the question of what to do in terms of allocating resources for emergency room physicians and urologists, CT scanners, lithotripters and other stone-related health care resources," Dr. Pearle commented.