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CD4-CD8 Ratio

Does this test have other names?

CD4/CD8 ratio T-cell test

What is this test?

This test looks at the ratio of two important types of white blood cells in your blood.

Lymphocytes are a type of white blood cell in your immune system. This test looks at two of them – CD4 and CD8. CD4 cells lead the fight against infections, and CD8 cells can kill cancer cells and other invaders.

If you have HIV, your CD4 cell count may be low. Without HIV treatment, your number of CD4 cells will likely continue to fall. A lack of CD4 cells usually leads to more frequent infection.

This test looks at the ratio of CD4 cells to CD8 cells. The ratio tells your doctor how strong your immune system is and helps predict how likely you are to develop a crippling infection.

In addition to HIV/AIDS, conditions that can be monitored with this test include infectious mononucleosis and other viral infections, chronic lymphocytic leukemia, Hodgkin disease, aplastic anemia, and neurological disorders like multiple sclerosis and myasthenia gravis. 

Why do I need this test?

You may need this test if your doctor suspects that you have HIV. Some people infected with HIV may develop flu-like symptoms within a few weeks of getting the virus, but other people have no symptoms at all.

Although the test looks at the ratio of CD4 cells to CD8 cells, your doctor may focus on the results of the CD4 count.

You may also have this test to see how well HIV treatment is working.

What other tests might I have along with this test?

Your doctor may also order other tests to help diagnose HIV. These include:

  • HIV test

  • Complete blood count

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results for the ratio are given as a number. The results for each cell count are given as a number per cubic millimeter (/mm3).

A normal CD4/CD8 ratio is 2.0, with CD4 lymphocytes equal to or greater than 400/mm3 and CD8 lymphocytes equal to 200 to 800/mm3.

If your ratio is higher than 2, it means your immune system is strong and you may not have HIV.

If your ratio is less than 1, you may have:

  • HIV

  • Bone marrow problems related to chemotherapy

  • Anemia

  • Multiple sclerosis, myasthenia gravis, or another nervous system condition

Higher than normal results may mean you have:

  • Major infection

  • Viral infection

  • Type of blood cancer

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Pregnancy can affect your results. Women with HIV may have higher levels of white blood cells, which affects the proportion of CD4 cells. Excessive use of alcohol can also affect your results. Certain medications, such as corticosteroids, that can affect your results.

How do I get ready for this test?

You don't need to prepare for this test. But tell your doctor if you are pregnant, are a heavy alcohol user, or are taking medications that could affect your white blood cell count. In addition, be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.