Jacobs Journal of Emergency Medicine

Incorporation of C - Reactive Protein Measurement into Alvarado Score Improves Model Performance

Published on: 2014-05-19


Objectives The aim of this study was to assess whether the incorporation of C-reactive protein (CRP) measurement into Alvarado Score may improve the appendicitis diagnosis performance. Methods A prospective observational study was carried out in the emergency department (ED) of a university hospital between July 2006 and June 2007. Adult patients presented to the ED with a provisional diagnosis of appendicitis were enrolled. Each patient underwent CRP and Alvarado score evaluation on admission. We added the CRP variable to the original Alvarado score and compared c-statistics, model fit, and calibration of the modified and original score. We also performed classification and reclassification tree (CART) analysis to see if the addition of CRP variable would improve discrimination. Results Of the 299 study patients, 198 (66.2%) had confirmed the diagnosis of appendicitis. Controlling for the Alvarado score and CRP elevation > 50 mg/L, was independently associated with acute appendicitis, justifying the addition of the CRP variable to the Alvarado score. Based on the beta-coefficient in the regression model, the CRP variable had a weight of 5 points. The area under the receiver operating characteristic (ROC) curve was 0.73 for original Alvarado score and 0.80 for CRP-modified Alvarado score. At an optimal cutoff point determined by ROC analysis (6 points), the Alvarado score had a sensitivity of 72.7% and a specificity of 63.4%. At a cutoff point of 9 points, the modified score had a sensitivity of 94.1% and a specificity of 46.5%. CART analysis created 2 decision trees for the diagnosis of appendicitis. The CRP-modified decision tree had an area under the curve (AUC) of 0.817, higher than that of the Alvarado score decision tree (AUC: 0.806). Conclusion Incorporation of CRP into the Alvarado score can improve the diagnostic performance of the Alvarado score. Future improvement of appendicitis diagnostic score should take into consideration the information of CRP. Limited by the small sample size, the results of this study require further external validation.