T-helper cells (CD4 cells) are white blood cells called lymphocytes and are part of the immune system. There are different T-cells that play a part in our immunity and are distinguished by certain receptors or antigens present on their outer membrane. The name CD4 comes from the CD4 receptor on the surface membrane of these cells. The name T-helper cell come from cell mediated immunity, where these cells induce an immune response to foreign pathogens or cancer cells. The CD4 T-helper cells provide immunity by activating cells to detect and destroy foreign antigens.
Although CD4 cells can be a protector, they are the main target of the HIV virus, which attaches itself to the CD4 receptor, enters the cell and inactivates it. As the HIV virus replicates and increases, the CD4 cell count will decrease. Once the CD4 cell count decreases below 500 cells/uL (normal healthy adults have >1000 cells/uL), patients will begin to receive anti-viral therapy.
CD8 cells, also known as cytotoxic T supressor cells, will identify and kill cells that are infected with a virus or are abnormal. When the virus enters the cell and begins to replicate and produce new viruses, they leave certain viral fragments behind. The CD8 cells specific for the antigens on these fragments will destroy the cell before it can create more virus. When a patient is having treatment for HIV, it is desirable to have an increase in CD4 and a decrease in CD8. Healthy patients normally have a CD4:CD8 ratio of >1.0. This means one or more CD4 cell per CD8 cell. In people with HIV, the ratio decreases, meaning that there are many more CD8 cells than CD4 cells. When the CD4 cell count decreases dramatically in a person infected with HIV, symptoms of AIDS will appear. This makes the CD4 and CD8 count very important in starting or changing anti-viral therapy. CD8 will increase in other cancers and infections other than HIV such as measles, burns or infectious mononucleosis.
The test for CD4/CD8 Ratio is used to help diagnose human immunodeficiency virus infection (HIV), to monitor patients with human immunodeficiency virus infection (HIV), and to make therapy treatment decisions in patient with human immunodeficiency virus (HIV). It is also used to help diagnose some other immunodeficiencies other than AIDS, and to monitor transplant patients.
The CD4 test is performed on a blood sample drawn from a vein in the patient’s arm. Additional tests may include complete blood count (CBC) with manual diff, CD3, HIV antibody screen, HIV western blot; HIV viral load; HIV genotypic resistance testing; HIV phenotypic resistance testing, and lymphocyte subset panel.
Reference ranges and specimen collection vary from test method and laboratories performing this test. To properly evaluate your test results, consult with the ordering physician or healthcare provider. If you would like to learn more about testing for CD4/CD8 Ratio click here for further information or you can research one of the references listed below.
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