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.