CD4 Cell Count and CD4 Percentage (T-Cell Test)

What is a CD4 cell count (T-cell test)?

A CD4 cell count is a blood test used to see how many of a particular type of white blood cell you have in a small amount of blood (about a drop). Healthcare providers use it to understand the impact HIV is having on your immune system and how well antiretroviral therapy (ART) is working. They sometimes use it to monitor other illnesses.

HIV is a lifelong viral infection that destroys CD4 cells (also called helper T-cells or CD4+ T-cells). A low T-cell count reduces your body’s ability to fight infections.

CD4 percentage

Your provider can also use CD4 percentage to help understand the health of your immune system. Providers figure out the CD4 percentage by dividing the number of CD4+ T cells by the total number of lymphocytes (a type of white blood cell) and then multiplying by 100.

CD4 percentage can be useful in situations where the absolute CD4 cell count may be less reliable. This could include having another condition that affects your total lymphocyte count, or in children, pregnant females and adults over 65.

What does CD4 count indicate?

CD4 counts give providers information about your immune system. CD4 counts outside of a normal range could indicate infections or other illnesses, or the progression of HIV.

CD4 counts can vary day-to-day due to the time of day your blood was drawn, whether or not you currently have an infection, and other factors. Your age, other health conditions, and the medicines you take can also influence what numbers are normal for you. This is why your provider looks at your total numbers as well as how your numbers are trending over time.

What are CD4 counts used for?

If you have HIV, healthcare providers use CD4 counts to:

• Determine how advanced an HIV infection is (staging)
• Monitor how well antiretroviral therapy is working
• Assess your risk for opportunistic infections (infectious diseases that usually only affect people with a weakened immune system)

A provider might also use T-cell tests to:

• Monitor anti-rejection medications after an organ transplant
• Monitor treatment for autoimmune diseases
• Diagnose illnesses, like certain types of lymphoma and DiGeorge syndrome

When are T-cell tests performed?

Your provider will test your CD4 counts when you’re first diagnosed with HIV. They’ll also use them to monitor your condition and how well your medications are working.

You might have to repeat CD4 cell count tests every three to six months when you first start ART medications. Over time, your provider might adjust that schedule to every six to 12 months. They’ll also use a viral load test to detect HIV levels in your body.

How does a CD4 cell count test work?

A lab technician uses a sample of your blood to determine your CD4 count. They count the T-cells in your blood sample using flow cytometry, which marks your cells with special labels.

How do I prepare for CD4 count test?

You don’t need to do anything to prepare for a CD4 test. You can eat and take medications as you usually would.

What should I expect during a CD4 count test?

A provider will use a small needle to take a sample of your blood from your arm. You might feel pain or discomfort briefly when the provider inserts and removes the needle. The provider will send the sample to a lab to perform the test.

What are the risks of a CD4 count test?

There are minimal risks of a CD4 test. Sometimes, a provider might need to stick your skin with the needle multiple times to find a vein, which can feel unpleasant. Blood draws also carry slight risks of:

• Feeling lightheaded or fainting
• A large bruise or blood collecting under your skin (hematoma)
• Infection
• Excessive bleeding

What kind of results do you get from a CD4 count test?

Providers report CD4 counts as the number of cells per cubic millimeter (a cubic millimeter is about the size of one drop of blood). This is usually written with the number followed by “mm^3” or “mcL” (microliters). You may also see CD4 counts as a percentage of lymphocytes (white blood cells).

Possible results include:

• Normal CD4 count: 500mm³ to 1,200mm³
• Low CD4 count: below 500mm³
• High CD4 count: above 1,200mm³

Some labs may use slightly different numbers for normal levels, especially the upper limit.

What does a low CD4 count mean?

If you have HIV, a low CD4 count means HIV has destroyed many of your white blood cells and weakened your immune system. You have an increased risk of infections, which can be life-threatening. A CD4 count at or below 200mm³ means you have stage 3 HIV (AIDS).

If you don’t have HIV, the following might cause a low CD4 count:

• Infection
• Cancer chemotherapy
• Medications that weaken your immune system (immunosuppressants)

What causes high CD4 counts?

Infections and some blood cancers can cause high CD4 counts (above the normal range).

When should I know the results?

Ask your provider when to expect results of your CD4 count and how you’ll get them. Providers often test blood within 24 hours of a blood draw, but it might take longer than that to get your results.

What happens if my CD4 count is low?

If your test results aren’t what your provider expects, they may repeat the test. Depending on your results, they might:

• Keep your treatment plan the same, but get your next CD4 count sooner than previously scheduled
• Prescribe medications (like antibiotics or antifungals) to help prevent infections if your immune system is significantly weakened
• Suggest changing what antiretroviral medications you’re on

When should I call my doctor?

Contact your provider if you have any questions about the results of your test. Go to the ER if you have signs of infection, including pain, swelling, pus or fever.

How can I increase my CD4 count?

Antiretroviral therapy is often very effective at reducing your viral load (amount of HIV in your body) and increasing your CD4 count. It needs to be taken consistently, so talk to your provider if you’re having a hard time taking ART.

In some cases, in people without HIV — like if you’ve had an organ transplant and are on immunosuppressive medications — having a low CD4 count might be an indication that your medications are working. Ask your provider what to expect.