a young red cell (erythrocyte) released by the bone marrow that contains no nucleus but has residual RNA; normally composes about 1% of circulating blood cells. The reticulocyte count is increased in hemolytic anemia.[close window

A red blood cell showing a reticulum or network when stained with vital dyes (for example, brilliant cresyl blue). The stage between the nucleated red cell and the mature erythrocyte.

The red cell for several days after it loses its nucleus in the marrow and for the first day of its life span in the blood contains leftover material that can be stained. In this way, the proportion of cells that are newly delivered into the blood from the marrow can be identified. Normally, a low proportion of reticulocytes (about 1% of red cells) are present in the blood. An increase in numbers indicates an increased production in the marrow, for example following blood loss, to replace lost blood cells.