Using ultrasonography (US) alone to detect kidney stones and determine their size may result in the inappropriate management of one-fifth of patients, investigators reported online in BJU International.
In a retrospective study of 552 stone patients comparing US with computed tomography CT)—the gold standard for diagnosing kidney stones—Vishnu Ganesan, BS, and colleagues at Cleveland Clinic in Ohio found that US had an overall sensitivity of 54%, although this increased with stone size. In addition, US significantly overestimated the size of stones in the 0–10 mm range. US had a specificity of 91%.
Stone location and patients’ body mass index did not significantly affect US sensitivity, a finding consistent with previous studies.
Assuming observational management would be recommended to patients with 0–4 mm stones and patients with 5 mm or larger stones could be counseled on the alternative of intervention, the investigators found that in 14% of cases where CT would suggest observation, US would lead to a recommendation for intervention. In contrast, when CT results would suggest intervention, US would suggest observation in 39% of cases, according to the investigators. On the basis of US alone, 22% of patients, on average, could have been inappropriately counseled.
Stones classified as 5–10 mm based on US had the highest probability (43%) of having their management recommendation changed when CT was performed, the investigators reported.
“The use of US for guiding management decisions for residual or asymptomatic calculi is limited because of its low sensitivity for smaller stones and its inability to accurately size the stone,” Ganesan and colleagues concluded. “As a result, one in five patients may be inappropriately managed when using US alone.”