en Gynecology & Obstetrics Gynecology & Obstetrics Original Research Original Research <p><strong>Background: </strong>Although acute appendicitis is a common problem, it remains a difficult diagnosis to establish, particularly among females of reproductive age. The present study was conducted to devise a new decision making model for diagnosing acute appendicitis in non-pregnant women.<br> &nbsp;&nbsp; <strong>Methods:</strong> The present study was a retrospective study consisting of women who had undergone an appendectomy between 2007 and 2015 at the emergency department of Imam Hossein Medical Center, Tehran, Iran. The inclusion criteria were being a female, presenting with abdominal pain, being a suspected case of acute appendicitis, and undergoing an emergency appendectomy. A classification and regression tree (CART) analysis was performed to partition exam and laboratory data obtained from these patients into homogeneous groups in order to develop a prediction rule for appendicitis diagnosis.<br> &nbsp;&nbsp; <strong>Results:</strong> The study population included 433 non pregnant women who underwent emergency operations with a preliminary diagnosis of acute appendicis. Out of these patients, 295 patients (68.1%) were appendicitis positive based on the pathology exam results, while 138 patients had a normal appendix, indicating a negative appendectomy rate of 31.8%. The final devised CART model included hemoglobin level, PMN count, age, and history of abdominal incision and yielded a sensitivity of 82.7% and specificity of 55.8%, which were better than Alvarado prediction results for the Asian population.<br> &nbsp;&nbsp; <strong>Conclusion:</strong> We have devised a simple and cost effective prediction model for predicting the outcome among non-pregnant women undergoing emergency appendectomy operation with good sensitivity and specificity compared to the Alvarado model.</p> Appendicitis, Prognosis, Decision Making, Model 732 736 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-6135-1&slc_lang=en&sid=1 Maliheh Arab drmarab@smbu.ac.ir 200319475328460063066 200319475328460063066 Yes Department of Gyneco-Oncology, Shahid Beheshti University of Medical Sciences, Tehran, Iran Behzad Nemati Honar nematihonar@gmail.com 200319475328460063067 200319475328460063067 No Department of Surgery, Shahid Beheshti University of Medical Sciences, Tehran, Iran Behnaz Ghavami behnaz_ghavami@yahoo.com 200319475328460063068 200319475328460063068 No Department of Laparoscopy, Tehran University of Medical Sciences, Tehran, Iran Robabeh Ghodssi-Ghassemabadi ghodsi@razi.tums.ac.ir 200319475328460063069 200319475328460063069 No Department of Biostatistics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Mahsa Aghaei dr.aghaee.m@gmail.com 200319475328460063070 200319475328460063070 No Shahid Beheshti University of Medical Sciences, Tehran, Iran Nasrin Yousefi ynasrin1990@yahoo.com 200319475328460063071 200319475328460063071 No Science and Research Branch, Islamic Azad University, Tehran, Iran Kourosh Sheibani sh_kourosh@hotmail.com 200319475328460063072 200319475328460063072 No Basir Eye Health Research Center, Tehran, Iran