Peripheral blood reticulocytes and their reference range values for percentage, absolute count, and immature fraction in children, measured with flow cytometry

Reticulocyte count by manual method has been the assay traditionally used to evaluate the status of erythropoiesis in hematological disorders with disturbances in erythropoietic activity. However, due to its variability, it is rather a semiquantitative method. Automated reticulocyte counting based on flow cytometry has provided more objective and exact measure of reticulocytes. Besides traditional parameters, such as percentage and absolute number of reticulocytes, automatic reticulocyte counters can detect differences in the amounts of cellular RNA present in immature erythrocytes that reflect their maturational stages and evaluate indices of reticulocyte maturation such as RMI, HFR, IRF. These parameters can be used as the earliest signs of marrow engraftment after autologous or allogeneic bone marrow transplantation. Currently there is no strict agreement between various automated methods of reticulocyte evaluation. Additionally, lack of standardization and quality control materials for this assay compels determination of own, interlaboratory ranges of reference values for new proposed parameters. A group of 102 children aged from 3 months to 18 years with normal hematological parameters was examined. Samples of blood stained supravitally with thiazole orange were analyzed in a flow cytometer. Results for percentage, absolute number and immature reticulocyte fraction expressed as a mean +/- 2SD were: 2.00 +/- 1.56%, 88.8 +/- 68.94 x 10(3)/microliter, and 0.22 +/- 0.16, respectively. A poor correlation was found between IRF and other parameters, suggesting its independent role as a marker of erythropoietic activity. Automated reticulocyte counting will probably improve the diagnosis and monitoring of many hematological diseases.