Reticulocytes

Reticulocytes are red blood cells that have yet to develop. They still contain hereditary material which is eventually lost during maturation. Erythtocytes, the final stage of red blood cells no longer contain RNA.
When someone is anemic, it is important to know if new red blood cells are being made. The absolute number of reticulocytes in the blood is an indication of the activity of the bone marrow that provides new red blood cells.
With increased production, the total number of reticulocytes will be increased. However, the amount in the bloodstream is measured and displayed as a percentage of red blood cells. This requires some reservation when interpreting the result. Because in the case of anemia, even if the total production of reticulocytes is not increased, an increased percentage of reticulocytes will be measured.

reference values: 0.5 - 2.0%.