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-Giemsa-stained smear and are referred to as polychromatophic red cells (image on the left). 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 for an actual count as seen in the image on the right.
