Reticulocytes, young red blood cells from which the nucleus has been lost, contain residual organelles (ie, ribosomes and mitochondria), which differentiate reticulocytes from mature erythrocytes. An elevated reticulocyte count is expected in sickle cell disease, thalassemia, spherocytosis, glucose-6- phosphate dehydrogenase deﬁciency, immune hemolytic disease, or hypersplenism. However, normal or decreased numbers of reticulocytes are measured in individuals with impaired erythropoiesis, for example, immunologic or drug-induced red blood cell aplasia; metastatic carcinoma; decreased erythropoietin production; and iron, folate, or B12 deﬁciency anemias.
The reticulocyte count is a useful tool in clinical studies of new patient therapies. It can be used to evaluate a patient’s responsiveness to vitamin supplementation, follow the progress of bone marrow transplant, or assess the impact of chemotherapies on hematopoietic function.
The amount of reticulocytes as a percentage of total erythrocytes in human peripheral blood samples can be identified by RNA staining, or by the presence of a surface marker, both measured by flow cytometry, as well as by Advia 120 analysis. The membrane permeable Retic-COUNT (Fig. 2) reagent binds RNA within the reticulocytes, forming a ﬂuorescent nucleotide-reagent complex. The fluorescently labeled antibody to human CD71 (Fig. 1) binds to the transferrin receptor, a membrane glycoprotein involved in iron transport, on the surface of the youngest reticuloyctes. The Retic-COUNT reagent and the antibody reagent are for in vitro diagnostic use only. The normal range of reticulocytes for adults is 0.6 - 2.7% of total erythrocytes with a mean of 1.5%. The reticulocyte count assay results are for research use only.
A blood sample stained with the anti CD71 antibody shows 9.4% of the cells are reticulocytes. The results are plotted with forward scatter (FSC-A) against the log of the fluorescence intensity of the antibody staining.
A second blood sample stained with the Retic-COUNT reagent shows 14.3% of the cells are reticulocytes. The results are plotted with forward scatter (FSC-A) against the log of the fluorescence intensity of the antibody staining.