Mohammad Rafeie - Department of Biostatistics, Faculty of Medicine, Arak University of Medical Sciences, Arak, Iran.
Naser Mohammad Gholi Mezerji - Department of Biostatistics, Public Health School, Hamedan University of Medical Sciences, Hamedan, Iran.
Zahra SHAYAN - Trauma Research Center, Department of Community Medicine, The Medical School, Shiraz University of Medical Sciences, Shiraz, Iran.
Ghasem Mosayebi - Department of Immunology and Microbiology, Faculty of Medicine, Arak University of Medical Sciences, Arak, Iran.

Objective: Appendicitis is a common cause of emergency hospitalization. White blood cell (WBC) counts are commonly used for the diagnosis of acute appendicitis in the early stages of pain; however, the effect of certain confounders, particularly age and sex, has been less focused. The purpose of the present study was to investigate the diagnostic accuracy of WBC in prediction of acute appendicitis using age-sex-adjusted Receiver Operating Characteristic (ROC) curve.Methods: In this cross-sectional study, 131 patients who had undergone appendectomy were studied during 2010-2011. Patients were placed in the normal appendix and acute appendicitis groups. ROC regression was used to identify the effects of the variables of age and sex on the diagnostic accuracy of WBCs using the area under the ROC curve (AUC).Results: Of the 131 patients, 81 (61.8%) were male and 50 (38.2%) were female. The mean age of the participants was years. Of the cases, 45 (34.4) had acute appendicitis while 86 (65.6%) were normal. In ROC regression, the AUC for WBC was 0.617 without adjustment for age and sex variables, 0.624 with an age-adjusted variable, 0.640 with a sex-adjusted variable, and 0.646 with both age- sex adjusted variables.Conclusion: Results indicated that in ROC regression analysis for the WBC test, age-sex adjusted variables increased the diagnostic accuracy of the WBC test for predicting acute appendicitis. Therefore, diagnosis of acute appendicitis is highly affected by confounding variables that we have to consider them with adjustment to achieve high accuracy in prediction of acute appendicitis.

Acute Appendicitis; Receiver Operating Characteristic curve; Regression; White Blood Cell count