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Computed Tomography and Ultrasonography To Detect Appendicitis
- Toshiya Shiga, MD, PhD;
- Zen'ichiro Wajima, MD, PhD; and
- 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.
When we compared Terasawa and colleagues' original figure with ours, it was apparent that the diagnostic performance of CT is superior to that of ultrasonography in cases of appendicitis. Terasawa and colleagues stated that in most of the studies they reviewed, appendiceal diameter greater than 6 mm was used as the positive diagnostic criterion for appendicitis. But, judging from their Appendix Table 2, most of the studies seem to have several criteria. However, both regression coefficients b are between −1.0 and 1.0 (P > 0.05), suggesting no significant variation in diagnostic performance with threshold. The diagnostic log odds ratios (logit transformation of the ratio of positive to negative likelihood obtained by the Mantel–Haenszel method) of CT and ultrasonography are estimated to be 5.0 (95% CI, 1.3 to 8.7) and 3.4 (CI, 0.9 to 5.9), respectively, indicating again that CT is superior to ultrasonography.
We also created a funnel plot to explore the publication bias. The funnel plot is asymmetric, indicating that publication bias is likely. It is possible that some studies of small samples that indicated low diagnostic accuracy for these tests were not published.
Our additional analysis does not mean that Terasawa and colleagues' conclusion needs alteration; rather, it strengthens their conclusion. They provided an elegant systematic review.
Toshiya Shiga, MD, PhD
Zen'ichiro Wajima, MD, PhD
Tetsuo Inoue, MD, PhD
Nippon Medical School, Chiba Hokusoh Hospital
Chiba 270-1613, Japan
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
Article and Author Information
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Potential Financial Conflicts of Interest: None disclosed.
