NEW YORK (Reuters Health) - Rates of kidney stones have increased substantially over the past 20 years, particularly among children, adolescents, females, and blacks, according to a population-based study in South Carolina.
Historically, the highest rates of kidney stone disease have been in middle-aged white men, but the new findings underscore emerging changes in this pattern. Prior studies have found that prevalent kidney stone disease has nearly doubled in the United States over the past two decades. The extent to which specific groups of patients have been affected has been less clear, although there have been reports of increasing frequency of kidney stones among youth.
"My colleagues and I wondered if kidney stones were increasing preferentially among adolescents more than in other age groups," lead researcher Dr. Gregory Tasian, of the University of Pennsylvania Perelman School of Medicine in Philadelphia, told Reuters Health by email.
To estimate the annual kidney stone incidence in South Carolina in their repeated cross-sectional study, the researchers used U.S. Census data and data from the South Carolina Medical Encounter Data and Financial Reports, which includes information on all surgeries, emergency department visits, and inpatient hospitalizations in the state from 1997 to 2012. Using linear mixed models, they also sought to identify the patient groups in whom the rate of stones has increased the most.
Nearly 153,000 adult and pediatric patients among a state population of about 4.6 million received care for kidney stones from 1997 to 2012, the researchers reported online January 14 in the Clinical Journal of the American Society of Nephrology.
The annual incidence increased 16% during that time, with the largest increases occurring in teens, blacks, and women. Teens 15 to 19 years comprised the age group with the largest increase in incidence of kidney stones from 1997 (an age-specific rate of nearly 80 per 100,000) to 2012 (about 155 per 100,000).
Overall, teens 15 to 19 experienced a 26% increase per five years (incidence rate ratio, 1.26), after adjusting for sex and race. The increase was substantially greater among teen girls,
with an annual incidence 52% higher than for teen boys.
Increases in cumulative risk of kidney stones during childhood were similar for girls (87%) and boys (90%), although the risks in 2012 were "modest," at 0.9% (for girls) and 0.6% (for boys), the researchers say. They note that the "emergence of nephrolithiasis as a disease that begins in childhood is worrisome because there is limited evidence about how to best treat children" with the condition.
After adjusting for age and race, incidence of kidney stones increased an estimated 15% per five years (IRR, 1.15) among females of all ages during the study period, but was stable among males (IRR, 0.99). The estimated lifetime risk for women increased from 10.5% in 1997 to 15.2% in 2012, but remained unchanged for men at about 23%. Incidence of kidney stones among blacks rose an estimated 15% per five years (IRR, 1.15) during the study period, compared with an estimated 3% among whites (IRR, 1.03).
"We were not surprised by the high occurrence of kidney stones among adolescents and females (5% and 3% per year), which is consistent with other studies reported to date," Dr. Tasian
said. "We were, however, surprised by how much kidney stones were increasing in African-Americans, as previous studies have not really studied differences in kidney stone occurrence among different racial groups."
Although the study focused on kidney stone disease in South Carolina, it's likely that similar patterns exist across the nation, he said.
"Kidney stones have increased 70% over the last 30 years in adults in the U.S., and we are also seeing higher rates of kidney stones in children across the U.S.," Dr. Tasian said.
However, even though kidney stones are also increasing in many areas in the world, for many reasons, the results should not be generalized beyond the United States, he noted.
"This study is an important step forward in understanding the changing epidemiology of kidney stone disease," Dr. Charles D. Scales, of Duke University Medical Center in Durham, North Carolina, told Reuters Health by email. The underlying causes of the increase are unclear. "In adults, it may be related to the tidal wave of obesity and diabetes in the United States," said Dr. Scales, an expert in kidney stones who was not involved with the study.
These epidemiologic trends provide more support for the concept that "chronic and poorly understood metabolic derangements are likely causing all of these new stones in previously low-risk individuals," he said.
Increased consumption of high-sodium processed food and dehydration also may be contributing factors, he added. "Emerging evidence suggests that a kidney stone may foreshadow future medical problems, such as heart disease, bone density loss, and chronic kidney disease," Dr. Scales said. "So from the public-health perspective, the worst may be yet to come as these teenagers with stones become adults."
The study had no commercial funding and the authors reported no disclosures.