Upper panel: In this anemic cat, there are numerous polychromatophils (arrows) and macrocytes (arrowhead) with a few normal RBC (N) in a Wright’s-stained smear of blood (Wright’s stain is a type of Romanowsky stain). Lower panel: The polychromatophils correspond to aggregate reticulocytes (arrows), whereas the macrocytes correspond to punctate reticulocytes (arrowheads). Normal RBC (N) lack any blue precipitated RNA (new methylene blue stain)(1000x magnification). Note, that only aggregate reticulocytes (which last for approximately 12 hours in circulation) would be included in a percentage or absolute reticulocyte count in cats. Thus, the degree of polychromasia (corresponding to these aggregate reticulocytes) is a good surrogate measure of the degree of reticulocytosis in this species.
