When the large reticulocytes usually found in the bone marrow are present in the peripheral blood, they are referred to as shift or stress reticulocytes. These cells may be up to twice the size of normal mature red cells and indicate the bone marrow's response to severe anemia.
These shift or stress reticulocytes are less mature than those typically in the peripheral blood. They contain more RNA than the more mature reticulocytes.
Advancements in automation in the hematology lab have made it possible to identify the presence of stress reticulocytes. This is often indicated by the immature reticulocyte fraction (IRF).
