Predictors of Nondiagnostic Ultrasound for Appendicitis.

BACKGROUND: Ionizing radiation and cost make ultrasound (US), when available, the first imaging study for the diagnosis of suspected pediatric appendicitis. US is less sensitive and specific than computed tomography (CT) or magnetic resonance imaging (MRI) scans, which are often performed after nondiagnostic US.

OBJECTIVES: We sought to determine predictors of nondiagnostic US in order to guide efficient ordering of imaging studies.

METHODS: A prospective cohort study of consecutive patients 4 to 30 years of age with suspected appendicitis took place at an emergency department with access to 24/7 US, MRI, and CT capabilities. Patients with US as their initial study were identified. Clinical (i.e., duration of illness, highest fever, and right lower quadrant pain) and demographic (i.e., age and sex) variables were collected. Body mass index (BMI) was calculated based on Centers for Disease Control and Prevention criteria; BMI >85th percentile was categorized as overweight. Patients were followed until day 7. Univariate and stepwise multivariate logistic regression analysis was performed.

RESULTS: Over 3 months, 106 patients had US first for suspected appendicitis; 52 (49%) had nondiagnostic US results. Eighteen patients had appendicitis, and there were no missed cases after discharge. On univariate analysis, male sex, a yearly increase in age, and overweight BMI were associated with nondiagnostic US (p < 0.05). In the multivariate model, only BMI (odds ratio 4.9 [95% CI 2.0-12.2]) and age (odds ratio 1.1 [95% CI 1.02-1.20]) were predictors. Sixty-eight percent of nondiagnostic US results occurred in overweight patients.

CONCLUSION: Overweight and older patients are more likely to have a nondiagnostic US or appendicitis, and it may be more efficient to consider alternatives to US first for these patients. Also, this information about the accuracy of US to diagnose suspected appendicitis may be useful to clinicians who wish to engage in shared decision-making with the parents or guardians of children regarding imaging options for children with acute abdominal pain.