A CD4 count is a test that measures the number of CD4 cells in your blood. CD4 cells, also known as T cells, are white blood cells that fight infection and play an important role in your immune system. A CD4 count is used to check the health of the immune system in people infected with HIV (human immunodeficiency virus).
HIV attacks and destroys CD4 cells. If too many CD4 cells are lost, your immune system will have trouble fighting off infections. A CD4 count can help your health care provider find out if you are at risk for serious complications from HIV. The test can also check to see how well HIV medicines are working.
A CD4 count may be used to:
- See how HIV is affecting your immune system. This can help your health care provider find out if you are at higher risk for complications from the disease.
- Decide whether to start or change your HIV medicine
- Diagnose AIDS (acquired immunodeficiency syndrome). The names HIV and AIDS are both used to describe the same disease. But most people with HIV don't have AIDS. AIDS is diagnosed when your CD4 count is extremely low. AIDS is the most severe form of HIV infection. It badly damages the immune system and can lead to opportunistic infections. These are serious, often life-threatening, conditions that take advantage of very weak immune systems.
You may also need a CD4 count if you've had an organ transplant. Organ transplant patients take special medicines to make sure the immune system won't attack the new organ. For these patients, a low CD4 count is good, and means the medicine is working.
Your health care provider may order a CD4 count when you are first diagnosed with HIV. You will probably be tested again every few months to see if your counts have changed since your first test. If you are being treated for HIV, your health care provider may order regular CD4 counts to see how well your medicines are working.
Your provider may include other tests with your CD4 count, including:
- A CD4-CD8 ratio. CD8 cells are another type of white blood cell in the immune system. CD8 cells kill cancer cells and other invaders. This test compares the numbers of the two cells to get a better idea of immune system function.
- HIV viral load, a test that measures the amount of HIV in your blood.
CD4 results are given as a number of cells per cubic millimeter of blood. Below is a list of typical results. Your results may vary depending on your health and even the lab used for testing.
If you have questions about your results, talk to your health care provider.Normal: 500–1,200 cells per cubic millimeter
While there is no cure for HIV, there are different medicines you can take to protect your immune system and can prevent you from getting AIDS. Today, people with HIV are living longer, with a better quality of life than ever before. If you are living with HIV, it's important to see your health care provider regularly.
Abnormal: 250–500 cells per cubic millimeter. It means you have a weakened immune system and may be infected with HIV.
Abnormal: 200 or fewer cells per cubic millimeter. It indicates AIDS and a high risk of life-threatening opportunistic infections.
A low CD4 count indicates that your immune system has been affected by HIV and/or the disease is progressing. At CD4 counts less than 200 cells/mm3, the immune system can no longer keep opportunistic infections in check. At low CD4 counts, a health care practitioner may recommend starting prophylactic treatment for opportunistic infections such as Pneumocystis carinii (jiroveci) pneumonia (PCP) or candidiasis (thrush). The Centers for Disease Control and Prevention (CDC) considers people who have an HIV infection and CD4 counts below 200 cells/mm3 to have AIDS (stage III HIV infection), regardless of whether they have any signs or symptoms.
What causes a CD4 count to drop?
CD4 cells are part of the immune system. They are present in blood cells and help protect the body from disease. When HIV enters body cells, it reproduces or makes copies of itself. As it does so, it causes CD4 cells to die, leaving the body more prone to infection and disease. Typically, the more virus that’s in the body, the lower the levels of CD4 will be, the more the immune system will be compromised, and the higher the person’s risk of infection. Antiretroviral treatment suppresses the virus and gives CD4 cells a chance to recover. As a person receives treatment, they can expect CD4 levels to rise. In the first year of antiretroviral treatment, one can expect typically to see a person’s CD4 count rise by 50–150 cells/mm3. After that, there will be slower yearly increases.
What are other factors that affect CD4 count?
HIV is not the only factor affecting CD4 levels. The following can also have an impact:
- Circadian rhythms, also called the body clock, vary during the day. One result of this is that CD4 levels tend to be lower in the morning and higher as the day progresses.
- Having an infection, such as the flu, pneumonia, or hepatitis B, can cause CD4 levels to fall.
- Some treatments, such as chemotherapy or single-dose steroids can cause CD4 levels to drop. However, ongoing steroid use may increase CD4 levels.
Other factors that may play a role include:
- nicotine or alcohol use
For this reason, there may be some variation in CD4 levels, even if a person’s health status has not changed. Also, the CD4 level will not affect how a person feels. Some people have low CD4 levels and function well, while others experience complications despite having higher levels.
Importantly, any single CD4 test result may differ from the last one even though your health status has not changed. Usually, a healthcare practitioner will take several CD4 test results into account rather than a single value and will evaluate the pattern of CD4 results over time.
The CD4 count tends to be lower in the morning and higher in the evening. Acute illnesses, such as pneumonia, influenza, or herpes simplex virus infection, can cause the CD4 count to decline temporarily. Cancer chemotherapy can dramatically lower the CD4 count.
The CD4 count does not always reflect how someone with HIV disease feels and functions. For example, some people with higher counts are ill and have frequent complications, and some people with lower CD4 counts have few medical complications and function well.
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