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Clinical Decisionmaking

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Computed tomography may be more accurate than ultrasound for diagnosing appendicitis in adults and adolescents

About 250,000 appendectomies are performed for acute appendicitis in the United States each year. Clinicians commonly use computed tomography (CT) or ultrasonography to diagnose acute appendicitis. However, CT is probably more accurate than ultrasound for diagnosing appendicitis in adults and adolescents, concludes a review of studies on the topic, which was supported in part by the Agency for Healthcare Research and Quality (K08 HS11291). C. Craig Blackmore, M.D., M.P.H., of the University of Washington, Seattle, and his colleagues conducted a meta-analysis of data from 22 prospective studies that compared results of CT, ultrasound, or both with surgical findings or clinical followup in patients 14 years of age or older with suspected appendicitis.

CT findings increased the certainty of diagnosis more than ultrasound. CT had a positive likelihood ratio of 13.3, indicating a large and often conclusive increase in the likelihood that patients with a positive test had appendicitis, versus ultrasound's positive likelihood ratio of 5.8, indicating a moderate increase in the likelihood that patients with a positive test had appendicitis. CT had an overall sensitivity of 0.94, meaning that 94 percent of patients with appendicitis had a positive test result, and a specificity of 0.95, meaning that 95 percent of patients who did not have appendicitis had a negative test result. Ultrasonography had an overall sensitivity of 0.86 and a specificity of 0.81.

The authors caution, however, that all studies had significant limitations that probably inflated estimates of diagnostic accuracy, such as inadequate blinding of the reference standard and pathologic verification of disease only in patients with positive test results. They call for prospective studies that apply gold standard diagnostic testing to all study participants to more reliably estimate the true diagnostic accuracy of these tests.

For more information, see "Systematic review: Computed tomography and ultrasonography to detect acute appendicitis in adults and adolescents," by Teruhiko Terasawa, M.D., Dr. Blackmore, Stephen Bent, M.D., and R. Jeffrey Kohlwes, M.D., M.P.H., in the October 2004 Annals of Internal Medicine 141, pp. 537-546.

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