The reticulocyte count is a measure of bone marrow productivity. It is the percentage of reticulocytes (newly formed red cells) in the peripheral blood. In the normal state, a reticulocyte spends 2-3 days in the marrow and 1 day in the peripheral blood before it loses its reticulum and becomes a mature red blood cell. The normal reticulocyte count is between 0.8 and 2.4% of the red cell number. Increase or decrease reflects red cell production by the bone marrow factory. If intense marrow stimulation occurs, larger stress reticulocytes or shift cells may be observed on the peripheral smear. These cells mature after 2 to 3 days in the circulation and may artificially inflate the reticulocyte count.
The reticulocyte count must be corrected for the reduction in red cell count to accurately reflect marrow production of erythrocytes. The most accurate correction is to determine the absolute reticulocyte count.