This study aimed to determine which children with suspected appendicitis should be considered for a computerized tomography (CT) scan after a non-diagnostic ultrasound (US) in the Emergency Department (ED).

We retrospectively reviewed patients 0–18year old, who presented to the ED with complaints of abdominal pain, during 2011–2015 and while in the hospital had both US and CT. We recorded demographic and clinical data and outcomes, and used univariate and multivariate methods for comparing patients who did and didn't have appendicitis on CT after non-diagnostic US. Multivariate analysis was performed using logistic regression to determine what variables were independently associated with appendicitis.

A total of 328 patients were enrolled, 257 with non-diagnostic US (CT: 82 had appendicitis, 175 no-appendicitis). Younger children and those who reported vomiting or had right lower abdominal quadrant (RLQ) tenderness, peritoneal signs or White Blood Cell (WBC) count >10,000 in mm³ were more likely to have appendicitis on CT. RLQ tenderness (Odds Ratio: 2.84, 95%CI: 1.07–7.53), peritoneal signs (Odds Ratio: 11.37, 95%CI: 5.08–25.47) and WBC count >10,000 in mm³ (Odds Ratio: 21.88, 95%CI: 7.95–60.21) remained significant after multivariate analysis. Considering CT with 2 or 3 of these predictors would have resulted in sensitivity of 94%, specificity of 67%, positive predictive value of 57% and negative predictive value of 96% for appendicitis.

Ordering CT should be considered after non-diagnostic US for appendicitis only when children meet at least 2 predictors of RLQ tenderness, peritoneal signs and WBC>10,000 in mm³.