A study of 5,047 asymptomatic adults who underwent a virtual colonoscopy found that the prevalence of urolithiasis—or urinary stone disease—in the study group was 8 percent, providing insight into the true prevalence of the disease, according to an article published in the March issue of the Journal of Urology

According to study author Cody Boyce, MD, University of Wisconsin School of Medicine and Public Health in Madison, and colleagues, urolithiasis counts for more than two million office visits and nearly 200,000 hospital admissions every year--at an estimated annual cost of more than $2 billion in the U.S. The authors noted that recent studies have suggested that the incidence of symptomatic stone disease is increasing.

Yet “despite the obvious importance of this disease, the true prevalence has not been established by objective criteria,” Boyce and colleagues wrote.

A number of different diagnostic methods are used for detecting urinary stones, but, according to the authors, “CT is clearly the diagnostic gold standard with an accuracy that approaches 100 percent due to the increased attenuation values of urinary calculi.”

For symptomatic patients with suspected urolithiasis, noncontrast CT also provides for rapid, accurate and noninvasive assessment, the researchers said, adding that because noncontrast CT evaluation of the entire urinary system is incidentally assessed at CT colonography (CTC) screening, “it provides an ideal means for determining the true prevalence of urolithiasis in an asymptomatic healthy adult population."

In this study, unenhanced low-dose CT was performed on 5,047 consecutive asymptomatic adults undergoing routine CTC screening at a single institution during a four-year interval between 2004 and 2008.

The study found that the prevalence of urolithiasis for the study population was 7.8 percent, of whom approximately 20 percent experienced symptoms during a 10-year interval, half of which occurred following asymptomatic detection at CT. The authors noted that similar studies have achieved similar results, suggesting “that this screening prevalence in asymptomatic adults may represent a generalizable result.”

Men (9.7 percent) were more likely to have urolithiasis than women (6.3 percent). “"Male gender showed only a modestly increased risk for symptom development, which was not statistically significant," the authors wrote. "However, because male gender showed a significantly higher underlying screening prevalence, this combination still led to a higher overall rate of previously detectable (i.e., symptomatic) urolithiasis."

Boyce and colleagues also found that established clinical risk factors such as diabetes, obesity and age, “did not show a significant increase in the screening prevalence of asymptomatic urolithiasis in our study.” Diabetes and obesity were associated, however, with a higher likelihood of symptomatic disease.

“The appropriate treatment of patients with these asymptomatic stones found incidentally at imaging remains uncertain,” wrote the authors. “ Because of the high asymptomatic prevalence and relatively low rate of symptomatic conversion within the entire cohort, initial conservative management may be appropriate, except for patients with a large stone burden, obstruction or comorbidities such as diabetes. Further investigation into the most appropriate clinical management of unsuspected urolithiasis is warranted.”