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The Test Sample
What is being tested?
Reticulocytes are newly produced, relatively immature red blood cells (RBCs). A reticulocyte test determines the number and/or percentage of reticulocytes in the blood and is a reflection of recent bone marrow function or activity.
Red blood cells are produced in the bone marrow, where blood-forming (hematopoietic) stem cells differentiate and develop, eventually forming reticulocytes and finally becoming mature RBCs. Reticulocytes are approximately 24% higher in volume in comparison with mature RBCs. Unlike most other cells in the body, mature RBCs have no nucleus, but reticulocytes still have some remnant genetic material (RNA). As reticulocytes mature, they lose the last residual RNA and most are fully developed within one day of being released from the bone marrow into the blood. The reticulocyte count or percentage is a good indicator of the ability of a person's bone marrow to adequately produce red blood cells (erythropoiesis).
RBCs typically survive for about 120 days in circulation, and the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. Normally, a stable number of RBCs is maintained in the blood through continual replacement of degraded or lost RBCs.
A variety of diseases and conditions can affect the production of new RBCs and/or their survival, in addition to those conditions that may result in significant bleeding. These conditions may lead to a rise or drop in the number of RBCs and may affect the reticulocyte count.
Higher than normal percentage of reticulocytes: Acute or chronic bleeding (hemorrhage) or increased RBC destruction (hemolysis) can lead to fewer RBCs in the blood, resulting in anemia. The body compensates for this loss or to treatment of deficiency anemias (such as iron deficiency anemia or pernicious anemia) by increasing the rate of RBC production and by releasing RBCs sooner into the blood, before they become more mature. When this happens, the number and percentage of reticulocytes in the blood increases until a sufficient number of RBCs replaces those that were lost or until the production capacity of the bone marrow is reached.
Lower than normal percentage of reticulocytes: Decreased RBC production may occur when the bone marrow is not functioning normally. This can result from a bone marrow disorder such as aplastic anemia. Diminished production can also be due to other factors, for example, cirrhosis of the liver, kidney disease, radiation or chemotherapy treatments for cancer, a low level of the hormone erythropoietin, or deficiencies in certain nutrients such as iron, vitamin B12, or folate. Decreased production leads to fewer RBCs in circulation, decreased hemoglobin and oxygen-carrying capacity, a lower hematocrit, and a reduced number of reticulocytes as old RBCs are removed from the blood but not fully replaced.
Occasionally, both the reticulocyte count and the RBC count will be increased because of excess RBC production by the bone marrow. This may be due to an increased production of erythropoietin, disorders that cause chronic overproduction of RBCs (polycythemia vera), and cigarette smoking.
Some drugs may increase or decrease reticulocyte counts.
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.