Computed Tomography and Ultrasonography To Detect Appendicitis

Toshiya Shiga; Zen'ichiro Wajima; Tetsuo Inoue

doi:10.7326/0003-4819-142-9-200505030-00022

Letters |3 May 2005

Computed Tomography and Ultrasonography To Detect Appendicitis

Toshiya Shiga, MD, PhD; Zen'ichiro Wajima, MD, PhD; Tetsuo Inoue, MD, PhD

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TO THE EDITOR:

We congratulate Terasawa and colleagues (1) for demonstrating the advantage of CT over ultrasonography in the diagnosis of acute appendicitis in adults and adolescents. We note that although they plotted the false-positive rate against the true-positive rate on their graph, they did not construct a summary receiver-operating characteristic (ROC) curve. The summary ROC curve, as described by Moses and colleagues (2), is a powerful tool for depicting diagnostic performance and showing how it is affected by the test threshold. Briefly, the regression model is expressed as D = a + b × S, where D is the diagnostic log odds ratio and S is the measure of how the test characteristics vary with the test threshold. We could not resist plotting summary ROC curves (figure not shown here) from Terasawa and colleagues' 2 × 2 contingency tables. We found that D = 5.2 − 0.49 × S for CT and D = 3.8 − 0.005 × S for ultrasonography.

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2005 American College of Physicians

Letters |3 May 2005

Computed Tomography and Ultrasonography To Detect Appendicitis

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Letters |3 May 2005

Computed Tomography and Ultrasonography To Detect Appendicitis

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