Asymptomatic Nephrolithiasis Detected by Ultrasound

Background and objectives: Data from several countries suggest a recent world-wide increase in the prevalence of stone disease. However, these studies have not analyzed the effect that increases in utilization of imaging modalities have had on detection of asymptomatic stones. Design, setting, participants, & measurements: A retrospective chart review of all patients who had an abdominal or retroperitoneal ultrasound in 2005 at a Department of Veterans' Affairs Medical Center was conducted. The charts of patients who had ultrasounds demonstrating kidney stones were further reviewed. Patients were classified into symptomatic and asymptomatic groups on the basis of their clinical history. Age and sex for all patients were recorded. For those patients with stones, additional data were recorded. Of all patients in the study, the percentage of those with asymptomatic stones was calculated. Taking into account uncertainty about symptomaticity in some patients, a sensitivity analysis for the presence or absence of gross and microhematuria was performed to determine a range for the percent of asymptomatic stones. Appropriate statistical tests were used to determine significance. Results: The prevalence of all kidney stones in the study group was 8.6%. Using the sensitivity analysis, 29.8 to 45.7% of all stones were asymptomatic. Of stones found on abdominal ultrasounds, 71.4% were asymptomatic, whereas 36.8% of stones found on retroperitoneal ultrasound were asymptomatic. Conclusions: Asymptomatic stones have a relatively high prevalence on ultrasound. Epidemiologic estimates of prevalence of nephrolithiasis need to account for increases in utilization of imaging modalities and the resulting detection bias.