SummaryBackgroundThe 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.MethodsThe 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.ResultsThe 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.ConclusionsThe results of our study, therefore, suggest that RET-He may be a clinically useful marker in the diagnosis of ID and IDA.