Influence of symptom duration and WBC profile on the negative predictive value of a nondiagnostic ultrasound in children with suspected appendicitis.

Background: The aim of this study was to explore the combined negative predictive value (NPV) of symptom duration and WBC profile in children with a nondiagnostic ultrasound (US) for appendicitis.

Methods: This was a retrospective analysis of children with suspected appendicitis at a single children's hospital from 1/2010 to 3/2018. NPVs based on WBC profile and symptom duration at presentation were calculated individually and combined for children with a nondiagnostic US.

Results: 2277 patients were included, of which 1018 (44.7%) had a nondiagnostic US. The NPV of a nondiagnostic US ranged from 83.7% with ≤24 h of symptoms to 94.5% with >72 h of symptoms (p < 0.01). NPV also differed significantly across WBC profiles, ranging from 76.8% when WBC profile was elevated to 97.3% to when WBC profile was normal (p < 0.01). The range of NPVs for a nondiagnostic US was even greater when combining symptom duration and WBC profile, ranging from 73.7% for patients with 24-48 h of symptoms and an elevated WBC profile to 100% for patients with >72 h of symptoms and a normal WBC profile.

Conclusions: Incorporation of symptom duration and WBC profile significantly improves the accuracy and clinical utility of the negative predictive value associated with a nondiagnostic ultrasound.

Level Of Evidence: Study of diagnostic test level II: development of diagnostic criteria in a consecutive series of patients and a universally applied gold standard.