• David S Huckins and Karen Copeland.
• Division of Emergency Medicine, Newton-Wellesley Hospital, Newton, MA, United States of America. Electronic address: dhuckins@partners.org.
• Am J Emerg Med. 2021 Jun 1; 44: 401-406.

ObjectivesTo assess the sensitivity, specificity, and negative predictive value (NPV) of normal total white blood cell count (WBC) and normal absolute neutrophil count (ANC) combined with a normal proprietary C-reactive protein (pCRP) level in adult emergency department (ED) patients with abdominal pain suspected of possible acute appendicitis.MethodsWe prospectively enrolled patients ≥18 years of age at seven U.S. emergency departments with ≤72 h of abdominal pain and other signs and symptoms suggesting possible acute appendicitis. Sensitivity, specificity, and NPV for normal WBC and ANC combined with normal pCRP were correlated with the final diagnosis of acute appendicitis.ResultsWe enrolled 422 patients with a prevalence of acute appendicitis of 19.1%. The combination of normal WBC and pCRP exhibited a sensitivity of 97.5% (95% CI, 91.3-99.3%), an NPV of 98.8% (95% CI, 95.9-99.7%) and a specificity of 50.0% (95% CI, 44.7-55.3%) for acute appendicitis. Normal ANC and pCRP resulted in a sensitivity of 100% (95% CI, 95.4-100%), a negative predictive value of 100% (95% CI, 97.5-100%) and a specificity of 44.4% (95% CI, 39.2-49.7%) for acute appendicitis. Normal WBC and pCRP correctly identified 171 of 342 (50.0%) patients who did not have appendicitis with 2 (2.5%) false negatives, while normal ANC and pCRP identified 150 of 338 (44.3%) of patients without appendicitis with no false negatives.ConclusionThe combination of normal WBC and ANC with normal pCRP levels exhibited high sensitivity and negative predictive value for acute appendicitis in this prospective adult patient cohort. Confirmation and validation of these findings with further study using commercially available CRP assays is needed.Copyright © 2020 Elsevier Inc. All rights reserved.

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