Purpose

The red cell goes through six different stages of development. The first four stages are normally confined to the bone marrow. The fifth (reticulocyte) and sixth (mature red cell) are found in both bone marrow and peripheral blood. Reticulocytes are immature non-nucleated cells that have a small network of basophilic organelles composed of RNA and protoporphyrin, which precipitate and appear blue with the new methylene blue stain. Reticulocytes may enter the peripheral blood circulation and persist for approximately 24 hours, revealing a faint gray blue hue or polychromatophilia.

The degree of reticulocytosis and the absolute reticulocyte count are an approximate measure of effective red cell production. A decreased marrow response may be seen with marrow damage, erythropoitin suppression, and deficient iron supply or with maturation disorders. An increased marrow response may be seen with hemolytic anemia, acute hemorrhage, and treatment with hematopoitic substances. Patients without anemia have approximately a 1% to 2% reticulocyte count. Reticulocyte count can be assessed by evaluating the level of polychromasia seen on a well stained peripheral slide.