Original ArticlesA 4-Year Investigation of Ambulatory Health Care Expenditure Concentration and High-Cost Patients An Experience From a Developing CountryEbrahimoghli, Reza MSc; Sadeghi-Bazargani, Homayoun MD, PhD; Janati, Ali PhD; Hamishehkar, Hadi PhD; Khalili-Azimi, Atefeh MScAuthor Information Department of Health Services Management, School of Management and Medical Informatics, Tabriz University of Medical Sciences, Tabriz, Iran (Mr Ebrahimoghli and Dr Janati); Road and Traffic Injury Research Center, Department of Statistics and Epidemiology, Faculty of Health, Tabriz University of Medical Sciences, Iran (Dr Sadeghi-Bazargani); Department of Clinical Pharmacy, Faculty of Pharmacy, Tabriz University of Medical Sciences, Iran (Dr Hamishehkar); and Department of Information and Technology, East Azerbaijan Health Insurance Organization, Tabriz, Iran (Ms Khalili-Azimi). Correspondence: Ali Janati, PhD, School of Management and Medical Informatics, Tabriz University of Medical Sciences, Daneshgah St, Tabriz, Iran (firstname.lastname@example.org). We hereby gratefully thank the authorities of East Azerbaijan Health Insurance Organization for accepting our request to use the claims database of the orga-nization.This study was funded by Tabriz University of Medical Sciences (grant number 60752). This study also has been approved by Research Ethics Committee of Tabriz University of Medical Sciences (approval ID: IR.TBZMED.REC.1397.559)The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Journal of Ambulatory Care Management: April/June 2020 - Volume 43 - Issue 2 - p 169-178 doi: 10.1097/JAC.0000000000000317 Buy Metrics Abstract The aim of this study is to investigate the concentration of ambulatory health care expenditure in a large Iranian outpatient population. This study used 2013-2016 individual-level claims data of Iranian Health Insurance Organization in East Azerbaijan province. All ambulatory care utilizers were included in the study. We determined characteristics and utilization pattern of high-cost patients as well as their predictors. A total of 1 128 149 patients were included. The top 10% of patients accounted for 62.56% of the total expenditure. This skewed expenditure pattern remained relatively stable over the study period. Female sex, older age, cancer, chronic obstructive pulmonary disease, cardiovascular disease, and diabetes increase the odds of being high cost. © 2019 Wolters Kluwer Health, Inc. All rights reserved.