Ultrasonography to Evaluate Adults for Appendicitis: Decision Making Based on Meta‐analysis and Probabilistic Reasoning

Abstract

Objectives: To review ultrasonography (US) test performance and to develop recommendations for the use of US to aid in the evaluation of potential appendicitis. Methods: A meta‐analysis was conducted using all English‐language articles published since 1986 (17 studies; 3,358 patients) to ascertain sensitivity and specificity of US for diagnosing appendicitis in adults and teenagers. Calculation of the predictive value of US was performed for three groups of patients: group I—usually operated on (prevalence of appendicitis = 80%); group II—usually observed in hospital (prevalence = 40%); and group III—usually released home (prevalence 2%). Results: Overall sensitivity was 84.7% (95% CI: 81.0–87.8%), and specificity 92.1% (88.0–95.2). The accuracy and usefulness of US were related to the likelihood of appendicitis. In group I, a positive test was accurate [positive predictive value (PPV) = 97.6%], but a negative study could not rule out appendicitis [negative predictive value (NPV) = 59.5%]. The converse was true for group III patients (PPV = 19.5%, NPV = 99.7%). Test performance accuracy was balanced only for group II patients (PPV = 87.3%, NPV = 89.9%). Conclusions: 1) US should not be used to exclude appendicitis for patients who have “classic” signs/symptoms, due to the underlying high false‐negative rate. 2) US is most useful for patients who have an indeterminate probability of disease after the initial evaluation—if US is positive, the patient should have an operation; otherwise, he or she should be observed. 3) US is not recommended for screening patients who have a low probability of appendicitis, due to the low prevalence of disease and high false‐positive rate in this group. © 1995 Society for Academic Emergency Medicine