What Is the CD4:CD8 Ratio Test Used For?
CD4 and CD8 are two types of white blood cells in your blood. White blood cells help your body fight infections.
CD4 cells and CD8 cells are named after proteins on their surface: CD4 cells have a protein called cluster of differentiation 4 (CD4), while CD8 cells have a protein called cluster of differentiation 8 (CD8). These cells are also called CD4+ and CD8+ cells, respectively.
The human immunodeficiency virus (HIV) chiefly targets CD4 cells. A low number of these cells and a low ratio (under 1.0) of CD4 and CD8 cells are signs of HIV infection. If you have an HIV infection, your CD4:CD8 ratio test results can help your doctor know how active the virus is in your body and how you're responding to your medicine.
Though it's mainly used to track your condition when you have HIV, your doctor may also use it for other conditions, such as:
- Mononucleosis or other viral infections
- Chronic lymphocytic leukemia
- Hodgkin's disease
- Aplastic anemia
- Multiple sclerosis
- Myasthenia gravis
Read on to learn a bit more about CD4 and CD8 cells, how the CD4:CD8 ratio test is done, and what your numbers may mean.
CD4 and CD8 Normal Ranges
CD4 and CD8 cells are both types of white blood cells called T cell lymphocytes. Some of your T cell lymphocytes direct other cells of your immune system on when and where to attack invaders, kind of like the General in a battle. One of these is your CD4, or helper T cells. They send out signals called cytokines that lead other immune system cells to the cells they need to attack.
Other T cells directly attack and kill foreign invaders. For instance, your CD8 cells (also called cytotoxic T cells) attack and kill cells that have been infected with viruses or bacteria. They can also kill cancer cells.
HIV specifically targets and kills your CD4 cells. This is why people with HIV tend to have low or very low numbers of CD4 cells. Also, your doctor may tell you to focus more on your CD4 numbers than your CD8 numbers when you get your CD4:CD8 ratio test results.
Different laboratories may have slightly different ranges they consider normal. This is because they may use different equipment to do the counts. Ask your doctor to go through your lab test results with you so you can understand the range your lab used and what your specific results mean.
Normal CD4 count
CD4 counts vary quite a bit between different people, even in people without HIV infection. Any factors that lead to an increase or decrease in your overall white blood cell counts affect your CD4 count. These factors include:
- Having an infection, inflammation, or injury
- Taking certain medicines
- Having a chronic condition
- Having advanced liver disease
- Having your spleen removed (splenectomy)
In many labs, a normal CD4 count ranges from 500 to 1,200 cells per milliliter of blood.
If your CD4 count is below 500 cells per milliliter of blood, you have a low CD4 count. If you have an HIV infection, a low CD4 count may mean that you're at a higher risk for infections. Your doctor may want you to take an antibiotic or antifungal to prevent these infections. If you don't have an HIV infection, a low CD4 count may mean you have another active infection in your body.
If you have an HIV infection and your CD4 count falls below 200 cells per milliliter of blood, your doctor will likely diagnose you with acquired immunodeficiency syndrome (AIDS). A CD4 count this low greatly increases your risk of developing life-threatening infections and cancer.
Normal CD8 count
A normal CD8 count generally ranges from 150 to 1,000 cells per milliliter of blood. Infection with HIV can cause your CD8 numbers to go up. However, because you may not have many CD4 cells to tell them where to go and what to do, these extra cells don't work very effectively to protect you from infections.
CD4:CD8 Ratio
The CD4:CD8 ratio test can help your doctor understand the strength of your immune system, especially if you have an HIV infection. They may use this test to:
- See if you're at risk of developing infections from viruses, bacteria, or fungi that people without HIV infection would probably clear on their own without treatment (opportunistic infections)
- Track how well your HIV treatment is working
- Diagnose you if your HIV infection has progressed to AIDS
Your doctor can also use this test to:
- Monitor your immune system when you're taking immunosuppressant medicines (usually taken after an organ transplant or in case of autoimmune conditions)
- Help diagnose certain types of lymphoma
- Help diagnose inherited conditions that may cause problems with your immune system, such as DiGeorge syndrome
The laboratory uses a special machine called a flow cytometer to measure your CD4 and CD8 numbers. The lab technician treats your blood cells with different fluorescent dyes that either stick to the CD4 or the CD8 proteins on the surface of these cells. Then, they run your cells through the flow cytometer, which uses a laser to detect the different dyes stuck on the surfaces of the different cells.
The lab that does the test calculates the CD4:CD8 ratio by dividing your CD4 cell count by your CD8 cell count. A ratio of 2 would show that you have two CD4 cells for every one of your CD8 cells. In general, having a higher ratio is better than having a lower ratio. The factors that affect your CD4 count therefore also change your CD4:CD8 ratio. Such factors include:
- Growing older (even in otherwise healthy people, the CD4:CD8 ratio tends to go down with age.)
- Having an infection, such as mononucleosis or tuberculosis
- Taking certain medicines, such as corticosteroids
- Natural variations in your body over the course of a year and even within a single day
What is a normal CD4 to CD8 ratio?
A CD4:CD8 ratio of 1 to 3 is considered normal. As long as your CD4 and CD8 counts are within an acceptable range, it shows that your immune system is strong and you aren't at a high risk for opportunistic infections.
If you have an HIV infection, your doctor will likely prescribe you antiretroviral therapy (ART). This helps keep the virus from multiplying in your cells. So, your CD4 cell count will gradually increase.
When your CD4 count is 500 cells per milliliter of blood or above, it's a sign that your HIV infection is under control. Your doctor will then likely have you get your CD4 count tested every three to six months while you're taking your ART medicine.
It may take several years of regular and consistent use of your medicine for your CD4 cell count to return to normal.
Low CD4:CD8 Ratio
A CD4:CD8 ratio less than 1.0 may show that you:
- Have an untreated HIV infection. After you're infected with HIV, your CD4 count may drop by about 30% and your CD8 count may rise by about 40%.
- If you're taking ART for HIV infection, your infection isn't yet under control.
- If you're taking chemotherapy medicines, you have issues with your bone marrow.
- Have anemia.
- Have multiple sclerosis, myasthenia gravis, or certain other nervous system conditions.
- Have a chronic infection.
For most people taking ART, your CD4 cell count is more important than your CD4:CD8 ratio, but your doctor may still use this test to help figure out if you're at a higher risk for cancer or may not respond to the vaccinations you need. So, they'll use this test to help guide your treatments.
High CD4:CD8 Ratio
Your CD4:CD8 ratio may be higher than 3 if you have:
- A serious bacterial infection
- A viral infection, such as with COVID-19
- Some types of blood cancer
Testing for HIV
You will usually have a CD4:CD8 ratio test to track how your treatment for HIV is working. But your doctor won't use this test to diagnose you.
Testing for HIV infection is generally using a couple of the following methods:
Antibody tests
Antibodies are proteins your immune system makes. Your body attaches them to materials from outside of your body, such as bacteria, fungi, viruses, and toxins, to let other cells in your immune system know to get rid of these materials.
Your lab technician will test your blood or spit for antibodies against HIV. Most of the rapid tests and HIV self-tests are also antibody tests.
Antigen/antibody tests
Your lab technician will test your blood for antibodies against HIV and also for proteins from the virus (antigen) in your blood.
Nucleic acid tests (NATs) or viral load tests
Your lab technician will test your blood for parts of the virus called nucleic acids. This test shows that you have the virus in your blood and also how much of it you have. This test can be expensive, so it's not usually used to test people for HIV infection. You're more likely to get this test if your doctor has already diagnosed you with HIV and they're monitoring how well your treatment is working.
High CD8 Count
Your CD4 counts may gradually go back to normal on ART treatment, but your CD8 counts may stay high, even when you're otherwise doing well.
No matter what your CD4 count, having a high CD8 count may increase your risk for:
- Long-term inflammation
- Cardiovascular disease
- Kidney disease
- Lung disease
- Diabetes or other metabolic conditions
- Some types of cancer
Your doctor may use your CD8 counts to track if you need treatments to help prevent some of these conditions.
Takeaways
The CD4:CD8 ratio test measures the ratio of two important types of white blood cells in your blood: CD4 cells and CD8 cells. Your doctor may order this test if you have an HIV infection to monitor how well your medicines are working and if your immune system is getting healthier. But you may also get this test as part of your checkups when you have cancer or certain autoimmune conditions. The normal CD4:CD8 ratio range is 1.0 to 3.0. If your ratio is less than 1.0, your doctor may need to prescribe you antibiotics or antifungals to help prevent opportunistic infections.
CD4:CD8 Ratio FAQs
What is the CD4:CD8 ratio for autoimmune disease?
There's no specific CD4:CD8 ratio that can diagnose an autoimmune condition. Your doctor will generally use a CD4:CD8 ratio test to help track your disease activity and maybe your risk for progression. If they do, they will need to understand how your CD4:CD8 ratio has changed over time. They won't rely on just one test result at one point in time.
