In a study, up to 45.7% of stones found on ultrasound examination fit criteria for being asymptomatic.

Ultrasound examinations turn up a relatively high prevalence of asymptomatic kidney stones, according to researchers.

David S. Goldfarb, MD, of the New York Harbor Veterans’ Affairs Medical Center and St. Vincent’s Hospital in New York, and colleagues reviewed abdominal and retroperitoneal ultrasound examinations of 1,220 patients.

Of these, 105 (8.6%) had kidney stones. In 48 (45.7%) of these patients, the stones fit criteria for being asymptomatic: the patients did not have stone symptoms at the time of the study and never had a symptomatic stone. This group included patients who had microhematuria found on urinalysis.

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When the investigators excluded microhematuria as a criterion for classifying stones as asymptomatic, the number of asymptomatic stones decreased to 31 (29.8%). “Therefore, among all ultrasounds that show nephrolithiasis, the prevalence of asymptomatic kidney stones can be reported as a range of 29.8[%] to 45.7%,” the authors wrote in the Clinical Journal of the American Society of Nephrology (2009;4:680-684).

Recent studies suggest an increasing prevalence of stone disease in the past three to four decades, the investigators noted, adding that these studies relied on patient questionnaires, hospital admission records, and large national health databases.

They pointed out, however, that “although factors such as changing diet and increasing prevalence of diabetes and obesity likely contribute to the observed epidemiologic trends, their relative effect on stone disease can only be assessed after accounting for increases in the use of imaging modalities.”

Based on study findings, Dr. Goldfarb’s group concluded that epidemiologic estimates of prevalence of kidney stones “need to account for increases in utilization of imaging modalities and the resulting detection bias.”

It is conceivable, the researchers observed, that imaging studies “find asymptomatic stones that are reported to patients who then can answer affirmatively to questions about stone prevalence when surveyed.”

The authors stated that one of the study’s limitations was the use of ultrasonography rather than noncontrast CT to assess the number of incidental stones. They noted that noncontrast CT is more sensitive for detecting stones and has largely replaced ultrasound imaging for evaluating patients with symptoms of acute colic. Therefore, CT may yield even a higher prevalence of asymptomatic stones than ultrasound-based studies.

In addition, because the study was retrospective, the researchers could not determine definitively if a patient was truly asymptomatic.