Reticulocytes are red blood cells that are still developing. They are also known as immature red blood cells. Reticulocytes are made in the bone marrow and sent into the bloodstream. About two days after they form, they develop into mature red blood cells. These red blood cells move oxygen from your lungs to every cell in your body.

A reticulocyte count (retic count) measures the number of reticulocytes in the blood. If the count is too high or too low, it can mean a serious health problem, including anemia and disorders of the bone marrow, liver, and kidneys.