Erythrocyte Indices as Differential Diagnostic Biomarkers of Iron Deficiency Anemia and Thalassemia Yeter Düzenli Kar, MD,* Zeynep C. Özdemir, MD,* Büşra Emir, MSc,† and Özcan Bör, MD* Introduction: The most common causes of microcytic anemia are iron deficiency anemia (IDA) and thalassemia trait (TT). This study investigated the reliability of erythrocyte indices and formulas as screening tests in the differential diagnosis of IDA and TT before performing detailed tests for definitive diagnosis. Materials and Methods: In total, 50 children with β-TT, 31 with α-TT, 50 with IDA were included. For the 8 erythrocyte indices and formulas (red blood cells [RBC], red blood cell distribution width [RDW], red blood cell distribution width index [RDWI], Mentzer index [MI], Shine and Lal index [S&L], England and Fraser [E&F], Green and King index [G&K], Srivastava index) the sensitivity, specificity, positive and negative predictive values (PPVs and NPVs, respectively) were calculated according to the cutoff values in the literature and recalculated revised cutoff values. Results: According to the cutoff values in the literature for the differential diagnosis of IDA and TT, the ranking of sensitivity, specificity, PPVs, and NPVs from the highest to the lowest was RDWI, RBC, E&F, G&K, MI, Srivastava, RDW, S&L. The sen- sitivity, specificity, PPVs, and NPVs of all the indices according to the revised cutoff values were higher than those according to the cutoff values in the literature. Conclusions: According to both the cutoff values in the literature and revised cutoff values, the most reliable indices were RBC and RDWI. Key Words: erythrocyte indices, iron deficiency, microcytic anemia, thalassemia trait (J Pediatr Hematol Oncol 2019;00:000–000) A nemia is characterized by hemoglobin (Hb), hematocrit (Hct), and erythrocyte counts that fall 2 SD values below the level accepted as normal for given age and sex. 1 Currently, it continues to be an important health problem, especially in developing countries. 2 According to the World Health Organization (WHO), it is reported that 30% of children in the 0 to 4 years age group and 48% of children in the 5 to 14 years age group are anemic in developing countries. 3 In Turkey, the most common types of microcytic anemia are iron deficiency anemia (IDA) and thalassemia trait (TT), and it has been estimated that there are ~1,300,000 β-thalassemia carriers (β-TT) in Turkey. 4 In 2 screening studies performed in the Adana province and its surroundings in southeastern Turkey, the newborn α-TT ratio was reported as 2.9% and 4.1%. 5 Iron deficiency in children may lead to a decrease in cognitive, behavioral, and motor functions. 6 Therefore, it is important to be able to distinguish IDA and TT and to treat IDA accordingly. 7 In contrast, unnecessary iron replace- ment therapy in thalassemia carriers without iron deficiency may lead to the risk of tissue and organ damage because of iron accumulation. 8 In studies conducted on children with hypochromic microcytic anemia, Ferrara et al 9 reported that none of the erythrocyte indices and formulas was sufficient for the dif- ferential diagnosis of iron deficiency and β-TT. Shen et al 10 found that the Green and King (G&K), Ricerca, and England and Fraser (E&F) indices were the most reliable indices for the differential diagnosis of IDA and β-TT in Chinese children. In contrast, Demir et al 11 reported that red blood cell (RBC) and red blood cell distribution width index (RDWI) were the most reliable indices, whereas Veahapoğlu et al 12 reported that Mentzer index (MI) was the most reliable index, and Narchi et al 13 reported that G&K index and red blood cell distribution width (RDW) were the most reliable indices for the differential diagnosis of IDA and α-TT. Standard tests for the differential diagnosis of micro- cytic anemia include complete blood count and iron and HbA 2 level measurements. If these tests fail to provide a diagnosis, genetic mutation analysis is then required for the diagnosis of α-TT. 1 Especially in primary health care pro- viders, it is possible to screen patients better using eryth- rocyte indices and formulas, which are easily available from blood counts. It should be kept in mind that these indices and formulas are not definitive diagnostic methods and that they cannot replace globin gene analysis. The aim of this study was to determine the efficacy of erythrocyte indices and formulas reported in the literature in distinguishing IDA and β-TT and IDA and α-TT in children with the hypochromic microcytic anemia. To this end, the reliability of erythrocyte indices and formulas in differential diagnosis was investigated according to both the cutoff values determined previously in the literature and the redetermined cutoff (revised cutoff) values calculated in this study. MATERIALS AND METHODS Subjects A total of 151 children who had been admitted to the Pediatric Hematology/Oncology Outpatient Clinic because of hypochromic microcytic anemia between January 2016 and October 2017 and who had been diagnosed with IDA and TT were included in the study. In this cross-sectional analytical study, the children were divided into groups Received for publication April 15, 2019; accepted August 5, 2019. From the *Department of Pediatrics, Division of Pediatric Hematology/ Oncology, Faculty of Medicine, Eskişehir Osmangazi University, Eskişehir; and †Department of Biostatistics, Faculty of Medicine, Izmir Katip Celebi, Izmir, Turkey. The authors declare no conflict of interest. Reprints: Yeter Düzenli Kar, MD, Department of Pediatrics, Division of Pediatric Hematology/Oncology, Faculty of Medicine, Eski şehir Osmangazi University, 26480 Eskişehir, Turkey (e-mail: yeterduzenli@yahoo.com). Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved. ORIGINAL ARTICLE J Pediatr Hematol Oncol  Volume 00, Number 00, ’’ 2019 www.jpho-online.com | 1 Copyright r 2019 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.