Also known as: T4 count, T-helper cells
Name: CD4
Related tests: Viral load
Why get tested?
To assess the strength of your immune system if you have been diagnosed with HIV infection
When to get tested?
If you have been diagnosed with HIV, to get a baseline picture of your immune system; four weeks after starting antiviral treatment and then every three months if you continue treatment
Sample required?
A blood sample taken from a vein in the arm
What is being measured?
The test measures the number of CD4 cells (also known as T-helper lymphocytes) in the blood, which is an indicator of the state of the immune system. CD4 cells are a type of white blood cell that fights infection and plays an important role in the immune system. They help identify, attack and destroy specific bacteria, fungi and other microorganisms that attack the body. CD4 cells are produced in the spleen, lymph nodes and thymus and circulate in the blood throughout the body. CD4 cells are the main target of HIV, which binds to the surface of these cells, enters them and either reproduces immediately, killing the cell, or remains latent and replicates later. As HIV enters cells and replicates, the number of CD4 cells in the blood gradually falls. If HIV disease progresses, the CD4 count will fall; if treatment slows the progression of the disease, the CD4 count will rise again.
How is the test result used?
When is it requested?
What does the result mean?
Is there anything else I should know?
How is the test result used?
The CD4 count tells the doctor how strong your immune system is and how far HIV disease has progressed (the stage of the disease), and helps predict the risk of complications and potentially debilitating infections. The CD4 count is even more useful when compared with an earlier count.
The CD4 count is used together with the viral load test, which measures the levels of HIV in the blood, to determine the stage and progression of the disease.
The CD4 count is also used to identify possible problems you may face and to establish which treatments may be most effective.
When is it requested?
The CD4 count and viral load are requested when a patient is diagnosed with HIV infection, to get a baseline picture. Both tests are repeated two to eight weeks after starting or changing antiviral treatment. If treatment continues, the test should be repeated every 3-6 months afterwards.
What does the result mean?
A normal CD4 count in an adult is 500-1500 cells per cubic millimetre of blood.
In general, the CD4 count falls as HIV infection progresses. A CD4 count may differ from the previous one even if your health has not changed. You should not attach too much importance to a single result. What matters more than a single result is the trend in CD4 over time.
If your CD4 count falls over several months, your doctor may consider starting or changing anti-HIV treatment and/or starting preventive treatment against opportunistic infections such as Pneumocystis pneumonia (PCP). Your CD4 count should rise or stabilise in response to effective anti-HIV treatment.
According to public health guidelines, preventive treatment should start when an HIV-positive person without symptoms has a CD4 count below 200. Some doctors choose to start treatment earlier, at 350. The Centers for Disease Control and Prevention consider HIV-positive people with a CD4 count below 200 to have AIDS, whether or not they feel well.
Is there anything else I should know?
CD4 counts tend to be lower in the morning and higher in the evening. Acute illnesses such as pneumonia, flu or herpes simplex virus infection can temporarily lower the CD4 count. Cancer chemotherapy dramatically reduces the CD4 count. Nevertheless, it is used as a valid monitoring tool if the more sensitive viral load test is not available.
The CD4 count does not always reflect how an HIV-positive person feels. For example, some people with higher counts are ill and have frequent complications, while others with lower values have fewer complications and function normally.