New Methylene Blue Stain, 500x

Reticulocytes in a canine blood smear

The reticulocyte is an immature red blood cell which has already lost its nucleus. With Wright's (or Romanowsky-based) stain, these cells are called polychromatophils and appear bluer than mature red blood cells. The New Methylene Blue stain reveals the ribosomes contained in the cytoplasm, allowing these cells to be more readily distinguishable. An elevated number of reticulocytes suggests an increased production of erythrocytes by the bone marrow,  in response to anemia. When anemia occurs, an evaluation of the number of reticulocytes is indicated in order to identify whether there is a bone marrow response and to classify the anemia. For the characteristics of feline reticulocytes, click here.