What Are Reticulocytes on a Blood Test?

What it means

Reticulocytes are red blood cells that have just left the bone marrow. They are slightly larger than mature red cells and still carry a little leftover material inside, which looks like a fine net when stained. That net gives them their name. Within a day or two in the blood they mature into ordinary red cells.

A reticulocyte count is usually ordered on purpose, often when someone has anemia. It tells the doctor whether the bone marrow is responding by making more red cells, or whether production is slow. That helps separate two broad situations: red cells being lost or destroyed, versus too few being made. It is also used to check the response after iron or vitamin treatment starts.

Reticulocytes are not the same as the red blood cell count (RBC), which counts all red cells, young and old. Some reports add a corrected count or a reticulocyte production index, which adjusts the result for how anemic the person is.

Where you may see it

• A separate line added to a CBC when the doctor requests it
• Hematology results labeled "Retic %" or "Retic absolute"
• Follow-up blood tests after treatment for iron deficiency or after bleeding