The reticulocyte is an immature but living red blood cell that has already lost its nucleus. They are formed in the bone marrow from stem cells to enter the bloodstream when they become red blood cells, replacing aged red blood cells. They are normally only present in small numbers in the blood, and in healthy people their percentage in the blood is stable. Reticulocytes circulating in the bloodstream contain a residue of genetic material (ribonucleic acid – RNA) that is lost in 1-2 days and they become mature red blood cells.
What does the test show?
By determining the number of reticulocytes and calculating the proportion present in the blood, it can be detected whether the red blood cell-forming function of the bone marrow is working properly, and the type and cause of anaemia can be established as well. Since the red blood cell count is used to determine the percentage of reticulocyte cells, the test is always ordered as part of a complete blood count.
In which cases is it recommended to perform the test?
Reticulocyte counts and percentages are usually ordered by your doctor to determine bone marrow function or to check the effectiveness of certain treatments (vitamin B12 or folic acid deficiency, iron deficiency, kidney disease, bone marrow suppression, erythropoietin therapy). The test is usually part of the general blood count.
The body tries to keep the number of red blood cells at a constant level, but if this balance is upset, the loss of red blood cells increases or their production decreases, anaemia develops. The cause and type of this can be detected by the test.
What sample is needed for the test?
A blood sample taken from a vein is needed for the test.
What can the result indicate?
The number of reticulocytes present in the blood reflects bone marrow activity.
If the reticulocyte count and ratio is higher than normal, it shows increased activity of the bone marrow to replace the red blood cells in the blood. This is common after major blood loss (accident, surgery), gastrointestinal bleeding (e.g. ulcers), a disease that causes red blood cells to break down, but it can also be a side effect of medicines after the red blood cells die. However, in case of iron deficiency anaemia, the effectiveness of the treatment is indicated by the increased number and proportion of reticulocytes. Elevated reticulocyte counts can also result from smoking, pregnancy, and the body’s adaptation to higher altitudes.
If the reticulocyte count is low, it indicates a malfunction of the bone marrow. This can be caused by bone marrow disease, a lack or inadequate absorption of vitamin B12 and folic acid, or inadequate production of the hormone erythropoietin produced by the kidneys.
What to do after the test?
The test alone cannot diagnose any disease, and in all cases consult an internist or haematologist to determine the exact diagnosis and therapy required.