The enumeration of peripheral blood reticulocytes is often performed to obtain information about the functional integrity of the bone marrow. Reticulocytosis occurs in anemic patients with a functional bone marrow and is marked by an increased number of peripheral blood reticulocytes, while reticulocytopenia occurs in anemic patients with a dysfunctional bone marrow and is marked by decreased numbers of peripheral blood reticulocytes. In addition to the evaluation of anemic patients, reticulocyte enumeration is also of value in monitoring bone marrow regenerative activity after chemotherapy or bone marrow transplantation. In the laboratory, the differentiation of the reticulocyte from the mature red blood cell is based on the presence of RNA and other substances in the reticulocyte, which are lost during differentiation into the mature red blood cell. Manual counting of reticulocytes by light microscopy with supravital dyes for RNA was developed in the 1940’s and remains the standard method of reticulocyte enumeration. However, reticulocyte enumeration by flow cytometry is much more accurate, precise, and cost-effective than manual counting and is increasingly being performed in the clinical laboratory. In addition, the flow cytometer provides a variety of additional reticulocyte-related parameters, such as the reticulocyte maturation index (RMI) and immature reticulocyte fraction (IRF), which are not available with light microscopy and appear valuable in the clinical diagnosis and monitoring of anemia and other diseases.(15.)
