A Reticulocyte (“Retic,” pronounced “reh-TICK”) is baby (immature) Red Blood Cell (RBC) made by our bone marrow, that hasn’t fully developed. It’s not seen on the common lab test “complete blood count (CBC),” and has to be ordered separately. We do this when a patient has Anemia (too few RBCs) and we’re trying to determine the type.
If a patient has ongoing very recent bleeding, there’ll be a high reticulocyte count as the body quickly tries to make new RBCs. If the blood loss is by hemolysis, disintegration of RBCs within our arteries & veins themselves, caused by certain uncommon diseases, then the Retic count is very high.
If anemia is due to a deficiency, like not enough iron, vitamin B12, or folic acid, necessary to make hemoglobin, then the Retic’s are low or “normal” (inappropriately not elevated in the face of anemia, when the body should try to make new RBCs, but can’t, because of the deficiency). With treatment of the deficiency, the reticulocyte count rises in a week (& we say the patient “is Reticking,” which is good).
If anemia is due to the bone marrow simply not making new RBCs, the reticulocyte count is low, or inappropriately “normal.” This is called “Anemia of Chronic Disease,” because we see it in chronic infections & diseases, but can also be due to medications & other causes. Such outside stressors inhibit bone marrow activity.
Many clinicians fail to order reticulocyte counts for anemic patients. Usually diagnoses can be made without them, but occasionally they can be surprisingly helpful.