NEW YORK - The number of children treated for kidney stones at some U.S. hospitals has been on the rise over the past decade, for reasons that are not yet clear, according to a new study.
Kidney stones develop when the urine contains more crystal-forming substances — including calcium, uric acid and a compound called oxalate — than can be diluted by the available fluid. The stones usually cause no lingering damage, but can be painful to pass.
While kidney stones are most common after age 40, they can develop at any age. And in recent years, there have been anecdotal reports from pediatric urologists and kidney specialists that they are seeing an increase in the number of children with kidney stones. One study published earlier this year showed that they were diagnosed in South Carolina kids four times as often in 2007 as in 1996, for unclear reasons.
But there has been a lack of hard data to show whether there is in fact a trend.
In the new government-funded study, researchers looked at data from 42 U.S. pediatric hospitals affiliated with the Child Health Corporation of America. They found that the number of children with kidney stones seen at the hospitals increased from 125 in 1999 to 1,389 in 2008.
That translated to a rate of 57 cases per 100,000 children treated at the hospitals in 2008 — up from 18 per 100,000 in 1999, the researchers report in the Journal of Urology.
It's not clear whether, or to what extent, the increase seen in the current study may reflect an upswing in kidney stones among U.S. children in general, according to Dr. Jonathan C. Routh and colleagues at Children's Hospital Boston.
The authors note that a recent study in Japan found no significant change in Japanese children's incidence of kidney stones between 1965 and 2005.
Because the figures come from children seen at a hospital, rather than a sample of children from the general population, they cannot be used to estimate the rate of kidney stones among U.S. kids, the researchers say.
The data, Routh told Reuters Health in an e-mail, "simply show that kidney stones are being more commonly treated at children's hospitals."
So it's possible, for instance, that doctors are more often referring children to hospitals for evaluation and treatment than they had in years past, Routh explained.
In recent years, more hospitals have opened pediatric kidney stone clinics. The current findings, Routh and his colleagues note, could have been partially driven by "intensified marketing" of stone-management services at the hospitals included in the study.
On the other hand, there are reasons to believe that more children may be developing kidney stones, according to Routh. Obesity is a risk factor for kidney stones, and the rising rate of childhood obesity in the U.S. could be at work. Since 1980, the percentage of obese kids between ages 6 and 11 has nearly tripled to 19.6 percent in 2008 according to the Centers for Disease for Disease Control and Prevention or CDC.
Diet is another potential culprit, Routh noted. Low fluid intake, and high intakes of sodium as well as animal fat and proteins, can contribute to kidney stones, he explained.
Children who have a family history of kidney stones or have ever had stones in the past are at greater risk of developing them than other kids are. Routh suggested that parents of these children, in particular, try to make sure their kids stay well-hydrated, especially during summer months.
Hydration, he said, is the best way to prevent stone formation in children at elevated risk.
Routh also pointed out, however, that despite the trend seen in this study and the fact that some children are at greater risk of kidney stones than others, "it's important to remember that kidney stones are still a rare event in children."