Background The prevalence of iron deficiency (ID) and iron deficiency anemia (IDA) in children with cancer is not well studied. The detection of ID and IDA using sensitive laboratory tools may facilitate early diagnosis and treatment in this cohort. In this regard, reticulocyte hemoglobin (Ret-He) content serves as a cost-effective measurement that remains unaffected by inflammation, unlike the ferritin test. Aim The objective of this study is to analyze the role of Ret-He as a diagnostic tool to identify functional and absolute ID and IDA in children with cancer. Methods We conducted a cross-sectional study in children aged 0 to 18 years. Blood samples were collected to compare Ret-He values with iron status, reflected by hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), serum iron (SI), total iron binding capacity (TIBC …