Wright's Stain, 500x

Polychromatophils in a canine blood smear

The polychromatophil is an immature red blood cell which has already lost its nucleus. It appears bluer than a mature red blood cell (colored with Wright's stain) and tends to be larger than the latter. However, when the blood is colored with the New Methylene Blue stain, polychromatophils are called reticulocytes because the stain highlights the ribosomes contained in their cytoplasm. An elevated number of polychromatophils suggests an increased production of erythrocytes by the bone marrow (erythroid hyperplasia) in response to anemia. Whenever anemia is present, a reticulocyte count is indicated in order to evaluate the bone marrow response and aid in classifying the anemia.