Reticulocyte Count

Also known as: Retic Count; Reticulocyte Index; Corrected Reticulocyte

Formal name: Reticulocyte Count

The Test Sample

What is being tested?

Reticulocytes are immature red blood cells (RBCs). They are produced in the bone marrow when stem cells differentiate and progress toward RBC development, eventually forming reticulocytes and finally mature RBCs. Most RBCs are fully mature before they are released from the bone marrow into the blood, but about 0.5 – 2% of the RBCs in circulation will be reticulocytes. This test measures the number and percentage of reticulocytes in the blood and serves as an indicator of the adequacy of bone marrow red blood cell (RBC) production.

Normal RBCs have a lifespan of about 120 days. The body attempts to maintain a stable number of RBCs in circulation by continually removing old RBCs and producing new ones in the bone marrow. If this steady state is disrupted by an increased loss of RBCs or by decreased production, then anemia will develop. Increased loss of red blood cells may be due to acute or chronic bleeding (hemorrhage) or hemolysis. The body compensates for this loss by increasing the rate of RBC production. When this happens, the number and percentage of reticulocytes in the blood increases until a sufficient number of RBCs are present and the balance is restored or until the production capacity of the marrow is reached.

Decreased RBC production may occur when the bone marrow is not functioning normally, due to a bone marrow disorder such as aplastic anemia or due to marrow suppression from a variety of causes including radiation and chemotherapy treatments for cancer, because of insufficient erythropoietin, or because of deficiencies in certain nutrients such as iron, vitamin B12, or folate. This decreased production leads to fewer RBCs in circulation, decreased hemoglobin and oxygen-carrying capacity, a lower hematocrit, and to a reduction in the number of reticulocytes as old RBCs are removed from the bloodstream, but not fully replaced.

Occasionally, both the reticulocyte count and the RBC count will be increased because of excess RBC production. This may be due to a variety of causes including inappropriately increased production of erythropoietin, disorders that chronically produce increased numbers of RBCs (polycythemia vera), and cigarette smoking.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or sometimes from pricking a finger or the heel of an infant.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.