At a Glance
Why Get Tested?
To help evaluate the bone marrow's ability to produce red blood cells (RBCs) and to help distinguish between anaemia related to blood loss or destruction and anaemia related to decreased RBC production; to help monitor bone marrow response and return of normal marrow function following chemotherapy treatment, bone marrow transplant, or post-treatment follow-up for iron deficiency anaemia
When to Get Tested?
A blood sample obtained by inserting a needle into a vein in the arm or sometimes from pricking a finger (or the heel of an infant)
The Test Sample
What is being tested?
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. Reticulocytes are immature red blood cells. They are produced in the bone marrow when stem cells differentiate to the next stage of 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.
The body attempts to maintain a stable number of RBCs in circulation by continually removing old RBCs (approximately 120 days old) 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 the affected patient will develop anaemia. Increased loss of red blood cells may be due to acute or chronic bleeding (haemorrhage) or haemolysis. 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 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 anaemia or due to marrow suppression from a variety of causes including radiation and chemotherapy treatments for cancer), because of insufficient erythropoietin (a hormone produced by the kidneys to stimulate RBC production) or because of deficiencies in certain nutrients such as iron, vitamin B12, or folate. This decreased production leads to decreased numbers of RBCs in circulation, decreased amounts of haemoglobin (an oxygen-carrying protein inside the RBC), a decreased haematocrit (the amount of cells versus plasma in the blood) and a decreasing 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 (polycythaemia vera), and even 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.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.