Although the nucleus has been extruded, the reticulocyte is still considered immature because it retains numerous organelles needed for hemoglobin production, such as ribosomes, mitochondria, and fragments of the Golgi apparatus. A reticulocyte normally remains in the bone marrow for one or two days before entering the circulation and its final 24 hours of maturation. The red cell is mature when hemoglobin production is complete and the organelles have disintegrated.
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 referred to as 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.
Automated methods are available for performing reticulocyte counts. An automated method provides a more accurate absolute reticulocyte count than the manual method that is reported as a percentage of total RBCs.