Reticulocytes are young erythrocytes which have just left the bone marrow and have not completely matured.
Although they are a little larger than normal erythrocytes and the central pallor is is just barely formed, reticulocytes cannot be identified by Wright staining. An important feature of their immaturity is the persistence of RNA, that can be verified with supravital staining. The reticular pattern that becomes visible in this staining played a role in the naming of reticulocytes.
Indicators of the presence of reticulocytes in the Wright staining are basophilc stippling and polychromasia. These are also caused by persistent RNA. Since reticulocytes are larger than normal erythrocytes, a pronounced reticulocytosis leads to an increased MCV (mean cell volume).
Reticulocytes usually constitute 0.5 to 2% of erythrocytes. Their normal range is - x 109/L. A reticulocyte count above the normal range is known as reticulocytosis.