Reticulocytes are immature red blood cells produced by bone marrow and released into the bloodstream. They circulate in the bloodstream for about 2 days before developing into mature red blood cells. Normally, about 1% to 2% of the red blood cells in the bloodstream are reticulocytes.

A reticulocyte count measures how rapidly reticulocytes are being made and released by the bone marrow. The reticulocyte count increases during rapid blood loss or in the course of certain diseases in which red blood cells are destroyed prematurely. Also, if a person spends an extended period of time at an elevation above sea level, reticulocyte counts may increase to help adapt to the lower oxygen levels found at high altitudes.

This test is done on a blood sample taken from a vein.

Reticulocyte Count
Results

Normal

The reticulocyte count is usually given as the percentage of red blood cells that are reticulocytes (the number of reticulocytes divided by the total number of red blood cells, multiplied by 100).

Normal values may vary from lab to lab.

Newborns have a normal reticulocyte count of 2.5% to 6.5%. This value drops within 2 weeks to 0.5% to 2.0%.

Greater than normal values may mean

• A high reticulocyte count may indicate increased production of red blood cells by the bone marrow, which can be caused by rapid blood loss, a move to high elevation, or certain types of anemia resulting in increased destruction of red blood cells (hemolysis).
• The reticulocyte count usually rises after successful treatment for pernicious anemia or anemia caused by a lack of iron (iron-deficiency anemia).

Lower than normal values may mean

• A low reticulocyte count may indicate decreased production of red blood cells by the bone marrow, which can be caused by aplastic anemia or other types of anemia.
• A low reticulocyte count can also be caused by exposure to radiation, a long-term (chronic) infection, or by certain medications that damage the bone marrow.