Validation and refinement of a prediction rule to identify children at low risk for acute appendicitis

Objective: To validate and refine a clinical prediction rule to identify which children with acute abdominal pain are at low risk for appendicitis (Low-Risk Appendicitis Rule). Design: Prospective, multicenter, cross-sectional study. Setting: Ten pediatric emergency departments. Participants: Children and adolescents aged 3 to 18 years who presented with suspected appendicitis from March 1, 2009, through April 30, 2010. Main Outcome Measures: The test performance of the Low-Risk Appendicitis Rule. Results: Among2625 patients enrolled, 1018 (38.8% [95% CI, 36.9%-40.7%]) had appendicitis. Validation of the rule resulted in a sensitivity of 95.5% (95% CI, 93.9%- 96.7%), specificity of 36.3% (33.9%-38.9%), and negative predictive value of 92.7% (90.1%-94.6%). Theoretical application would have identified 573 (24.0%) as being at low risk, misclassifying 42 patients (4.5% [95% CI, 3.4%- 6.1%]) with appendicitis. We refined the prediction rule, resulting in a model that identified patients at low risk with (1) an absolute neutrophil count of 6.75 × 103/μL or less and no maximal tenderness in the right lower quadrant or (2) an absolute neutrophil count of 6.75 ± 103/μL or less with maximal tenderness in the right lower quadrant but no abdominal pain with walking/jumping or coughing. This refined rule had a sensitivity of 98.1% (95% CI, 97.0%-98.9%), specificity of 23.7% (21.7%-25.9%), and negative predictive value of 95.3% (92.3%-97.0%). Conclusions: We have validated and refined a simple clinical prediction rule for pediatric appendicitis. For patients identified as being at low risk, clinicians should consider alternative strategies, such as observation or ultrasonographic examination, rather than proceeding to immediate computed tomographic imaging.