Abstract
The immature reticulocyte fraction (IRF) reflects early erythropoietic activity and is used to monitor hematopoietic function clinically. However, the physiological behavior of the IRF in healthy individuals of different ages has not been thoroughly investigated. This study evaluates age-related variations in the IRF and its correlations with hematological parameters across a wide age spectrum in healthy individuals. This cross-sectional study included 853 healthy individuals categorized into 6 age groups: <8 days, 8 to 30 days, 30 days to 1 year, 1 to 16 years, 16 to 55 years, and >55 years. Correlation analyses were performed using data obtained from a high-precision hematology analyzer (Sysmex XN-Series), which applies fluorescence flow cytometry and impedance technology for reticulocyte quantification, to examine the correlation between IRF and hematological parameters (hemoglobin [Hb], HCT [hematocrit], red blood cell count [RBC], white blood cell count, red cell distribution width, reticulocyte hemoglobin content, reticulocyte percentage, and leukocyte subtypes). IRF levels showed significant differences between age groups (P < .001). In neonates group, IRF showed a positive correlation with white blood cell count (r = 0.64, P < .001) and neutrophil count (r = 0.65, P < .001). The negative correlation with Hb and RBC became more pronounced in older age groups (Hb: r = -0.43; RBC: r = -0.32; P < .001). A positive and significant relationship with red cell distribution width was observed in all age groups (r = 0.30-0.54, P < .001). IRF shows different age-related connections with hematological parameters. These connections reflect the changing dynamics of erythropoiesis and bone marrow activity throughout life. Using age-specific reference frameworks to incorporate IRF into clinical assessments may improve the detection and interpretation of subclinical changes in erythropoietic function.