Reticulocytes are relatively immature young red blood cells. A reticulocyte count indicates the number of reticulocytes per litre of blood. Functional bone marrow compensates for a decreased red blood cell count by producing more reticulocytes and releasing them earlier into the blood. The presence of reticulocytes therefore indicates that the bone marrow is capable of producing red blood cells, an important factor in the diagnosis and monitoring of different causes of anemia.
A high reticulocyte count should be found in anemias caused by acute or chronic bleeding (external or internal bleeding such as digestive bleeding) or by the accelerated destruction of red blood cells (hemolytic anemia). A high count would also be appropriate during the treatment for iron deficiency anemia or pernicious anemia.
An abnormally low reticulocyte count may indicate impaired bone marrow function as in the case of aplastic anemia (non-functional bone marrow), or it may be caused by cirrhosis of the liver, kidney disease, radiation therapy or chemotherapy for cancer, low erythropoietin levels or an untreated iron, folic acid or vitamin B12 deficiency.