Although the nucleus has been extruded, the reticulocyte is still considered an immature erythrocyte because it retains numerous organelles needed for hemoglobin production, such as ribosomes, mitochondria, and fragments of the Golgi apparatus. A reticulocyte typically remains in the bone marrow for one or two days before entering the circulation and its final 24 hours of maturation. When hemoglobin production is complete, the red cell matures, and the organelles disintegrate.
The reticulocyte is slightly larger (10 microns) than the mature erythrocyte. Reticulocytes appear blue-gray on the Wright or Wright-Giemsa-stained smear and are called polychromatophilic red cells (indicated by the arrow in Image A). The residual RNA in the cytoplasm causes the blue-gray color. A supravital stain, such as new methylene blue N or brilliant cresyl blue, is used to stain reticulocytes (indicated by the arrows in Image B) for an actual count.
It is important to note that while polychromatophilic red cells are most likely reticulocytes, they should not be indicated as reticulocytes until a supravital stain has been used. In evaluating red cell morphology on a peripheral blood smear, polychromatophilic red cells should be noted as such, not as reticulocytes.
Automated methods are available for performing reticulocyte counts. An automated method provides a more accurate absolute reticulocyte count than the manual method, which reports as a percentage of total RBCs.
