If someone has received an HIV diagnosis, there are two things they’ll want to know: their CD4 count and their viral load. These values give them and their healthcare team important information about:

  • the health of their immune system
  • the progression of HIV in their body
  • how their body responds to HIV therapy
  • how the virus itself responds to HIV therapy

The aim of treatment is to raise the CD4 count and lower the viral load. When viral levels become undetectable, the virus is no longer transmittable during sexual activity, according to the Centers for Disease Control and Prevention (CDC).

Regular testing can also ensure levels stay undetectable, and this can boost the person’s quality of life.

A CD4 count is a blood test to check the amount of CD4 cells in the body. CD4 cells are a type of white blood cell. They play a key role in the immune system. They alert other immune cells to the presence of infections such as bacteria and other viruses in the body. CD4 cells are also a subset of immune cells called T cells.

When a person is living with HIV, the virus attacks the CD4 cells in their blood. This process damages CD4 cells and causes a drop in the number of them in the body, making it difficult to fight infections. Monitoring CD4 cells is important for people who are receiving treatment for HIV.

CD4 counts vary widely. For many people, however, the higher a CD4 count is when they receive a diagnosis and start treatment, the more quickly they are likely to see it rise as a result of therapy. This is one reason why an early diagnosis is essential.

The chart below summarizes the ranges of CD4 counts:

CD4 countMeaning
500–1,600 cells/mm3Most people without HIV have this level.
250–500 cells/mm3The immune system is compromised, and one reason could be HIV.
Under 200 cells/mm3A doctor will diagnose AIDS.

CD4 counts show the robustness of the immune system. A healthy immune system normally has a CD4 count ranging from 500 to 1,600 cells per cubic millimeter of blood (cells/mm3), according to HIV.gov.

When a CD4 count is lower than 200 cells/mm3, a person will receive a diagnosis of AIDS. AIDS is a separate condition that can develop in a person with HIV. It is also called stage 3 of HIV. At this stage, the body’s immune system is weak due to the low number of CD4 cells available to fight disease, and the person’s risk of infection is very high.

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, you 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:

  • stress
  • fatigue
  • nicotine or alcohol use
  • pregnancy

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.

An HIV viral load test measures the number of HIV particles in a milliliter (mL) of blood. These particles are also known as “copies.” The test assesses the progression of HIV in the body. It’s also useful in seeing how well a person’s HIV therapy is managing the virus in their body.

A person may have a high viral load soon after contracting HIV or if treatment is not proving effective. When a person first contracts the virus, levels will rise significantly, but in the next 3 to 8 weeks, the body starts to produce antibodies. This can reduce the virus levels. A viral load can include over a million copies per mL of blood, especially after recent exposure, according to an observational study of data published in 2018.

Effective treatment will result in viral suppression. This is when there are fewer than 200 copies/mL. At this stage, the risk of HIV progressing is low, but the virus is still present A person can still pass on the virus.

As treatment progresses, the viral load can become so low that it is undetectable in a test. An undetectable viral load will be under 40 to 75 copies in a blood sample. This means there are relatively few copies of HIV in the blood.

When this happens, it is no longer possible to pass the virus on to another person during sex, according to the CDC. An undetectable amount of HIV is untransmittable.

However, continued treatment is necessary to ensure the viral load remains undetectable.

There’s no direct relationship between CD4 count and viral load.

In the past, doctors used the CD4 count as an indicator of when to start therapy, but advances in HIV medication have changed this. Now it serves as an indicator of immune system stability.

However, in general, a high CD4 count and a low — or undetectable — viral load are desirable. The higher the CD4 count, the healthier the immune system. The lower the viral load, the likelier it is that HIV therapy is working.

When HIV invades healthy CD4 cells, the virus uses them to make new copies of HIV before destroying them. When HIV remains untreated, the CD4 count decreases, and the viral load increases.

The following chart gives a general idea of what the levels of CD4 and viral load mean for a person with HIV, based on guidelines from the U.S. Department of Health and Human Services.

How serious is this?CD4 levelViral load
A person needs medical attention and will need prophylactic medications to prevent opportunistic infections.200 cells/mm3over 200 copies/mL
Monitoring is essential, but a doctor may consider levels stable.300–500 cells/mm3 less than 200 copies/mL
Acceptable levels.500–1,500 cells/mm3less than 20–75 copies/mL

Most people living with HIV will have regular CD4 and viral load tests, but the frequency will vary, according to how their treatment progresses and how their body responds to it.

How often should you test your CD4 counts?

Most people will need a test every 3 to 6 months, according to the U.S. Department of Health and Human Services.

More frequent testing may be needed if:

  • you are just starting treatment
  • you change medications
  • your have a viral load that is difficult to suppress
CD4 statusNeed for testing
Most people with detectable virus.Every 3–6 months
HIV responds well to treatment, and CD4 levels have been stable between 300–500 cells/mm3 for 2 years.Every 12 months
Viral load remains undetectable, and CD4 counts are over 500 cells/mm3 for 2 years.May be optional

However, if any change occurs in the person’s health or treatment status, the doctor will review the testing schedule.

How often should you test your viral load counts?

The frequency of testing will depend on how soon after the diagnosis it is, the treatment, and how well the body is responding.

Current guidelines provided by HIV.gov recommend the following intervals for testing:

StatusFrequency of testing
The person has just started antiretroviral treatment or their doctor has changed their treatment.After 2–8 weeks
Until the viral load becomes undetectable.Every 4–8 weeks
While the viral load is stable.Every 3–4 months
After levels remain stable for 2 years.Up to 6 months interval

Why is it important to get tested regularly?

CD4 and viral load testing can help you and your doctor understand:

  • how well treatment is working
  • your risk of developing an opportunistic infection
  • the risk of HIV progressing to AIDS

The results can guide decisions about future testing and treatment strategies.

Can you test at home?

There is currently no CD4 testing at home, and a doctor would need to interpret any results, as they would need to take other factors into account. Doctors also prefer to use the same testing facilities to ensure consistency.

In some countries, point-of-care testing is available. The CDC is looking into this option for the United States, but it’s not yet available.

A single CD4 or viral load test result only represents a snapshot in time. It’s important to track both of these and consider trends in test results rather than only looking at individual test results.

Keep in mind that these values may vary for many reasons. The time of day, any illnesses, and recent vaccinations can all affect CD4 count and viral load. Unless the CD4 count is very low, this fluctuation isn’t usually worrisome.

Regular viral load tests, not CD4 counts, are used to determine the effectiveness of HIV therapy. The goal of HIV therapy is to reduce or suppress the viral load to an undetectable level.

According to HIV.gov, HIV viral load is typically undetectable below levels of 40 to 75 copies/mL. The exact number depends on the lab that analyzes the tests.


Some people may experience blips. These are temporary, oftentimes small increases in viral load. A healthcare professional will monitor the viral load more closely to see if it returns to an undetectable level without any change in therapy.

Drug resistance

Another reason for regular viral load tests is to monitor any drug resistance to the prescribed HIV therapy. Maintaining a low viral load reduces the risk of developing resistance to the therapy. A healthcare professional can use viral load tests to make necessary changes to a person’s HIV therapy regimen.

HIV therapy is also called antiretroviral therapy or highly active antiretroviral therapy (HAART). It consists of a combination of antiretroviral drugs. They’re designed to keep the virus from spreading throughout your body by targeting different proteins or mechanisms the virus uses to replicate.

Antiretroviral therapy can make the viral load so low that it can’t be detected by a test. This is called an undetectable viral load. If a person is virally suppressed or has an undetectable viral load, their HIV is well managed.

Starting HIV therapy as soon as an HIV diagnosis is received helps allow a person to live a long, healthy life.

Current treatment guidelines provided by the U.S. Department of Health and Human Services recommend that a person living with HIV begin antiretroviral drugs as soon as possible after diagnosis. This is essential to reducing opportunistic infections and preventing complications from HIV.

Effective treatment can also help prevent the transmission of HIV to others. This is also known as “treatment as prevention.”

According to the CDC, people with HIV who take their prescribed medications and maintain an undetectable viral load have “effectively no risk” of transmitting HIV during sexual activity.

No matter the stage of HIV, there are advantages to keeping track of the CD4 count and viral load.

HIV treatment has come a long way in recent years. Following a recommended treatment plan and leading a healthy lifestyle can help a person keep their CD4 count high and their viral load low.

Early treatment and effective monitoring can help a person manage their condition, reduce their risk of complications, and live a long and healthy life.