© 2019 Mehmet Ali Uçar, Mesude Falay, Simten Daǧdas, Funda Ceran, Selin Merih Urlu, Gülsüm Özet published by Sciendo.The purpose of this study is to investigate whether or not reticulocyte hemoglobin equivalent (RET-He) is a superior indicator of blood count and other iron parameters in terms of diagnosing iron deficiency (ID) and iron deficiency anemia (IDA), and thus evaluating a patient's response to oral iron treatment. The research population consisted of 217 participants in total: 54 control, 53 ID, 58 non-ID anemia, and 52 IDA patients. A hemoglobin (Hb) value of < 130.0 g/L was defined as indicating anemia for men, while an Hb value of < 120.0 g/L was defined as indicating anemia for women. All patients were administered 270 mg oral elemental iron sulphate daily. The RET-He was significantly lower in the IDA group, compared to other groups (IDA: 21.0 ± 4.1, ID: 26.0 ± 4.9, non-ID anemia: 32.1 ± 6.8, control: 36.6 ± 7.0; < 0.001). The ID group had a lower RET-He compared to the non-ID anemia group and the control group. On the 5th day of treatment, the ID and IDA group showed no significant differences in terms of Hb while the RET-He level demonstrated a significant increase. The increase in the RET-He level observed in the IDA group on the 5th day was significantly higher compared to the increase observed in the ID group. A RET-He value of 25.4 pg and below predicted ID diagnosis with 90.4% sensitivity and 49.1% specificity in IDA patients, compared to the ID group. The results of our study, therefore, suggest that RET-He may be a clinically useful marker in the diagnosis of ID and IDA.