Key takeaways
- CD4 counts and viral load measurements help monitor HIV and how well treatment is working. The goal is to increase CD4 counts and decrease viral load.
- A low CD4 count indicates a weakened immune system and a higher risk of infection, while a high viral load means there are many copies of HIV in the blood.
- Regular testing of CD4 count and viral load helps healthcare teams make informed decisions about treatment and assess the risk of HIV progressing or transmitting to others.
If someone has received an HIV diagnosis, there are two pieces of health information that are important for them to know: their CD4 count and their viral load. These numbers 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 HIV treatment is to raise the CD4 count and lower the viral load. When viral levels become
A CD4 count is a blood test to check the number 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 has HIV, the virus attacks the CD4 cells in their blood. This process damages CD4 cells and causes a drop in the number of these cells 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 typically see it rise as a result of therapy. This is one reason why an early diagnosis is essential.
The chart below summarizes CD4 count ranges (measured in cells per cubic millimeter), per the HIV.gov website:
| CD4 count (cells/mm3) | Meaning |
| Above 500 | Most people without HIV have this level. |
| 250 to 500 | The immune system is compromised. One reason could be HIV. |
| Below 200 | A healthcare professional will typically diagnose stage 3 HIV, also referred to as AIDS. |
CD4 counts show the robustness of the immune system. A healthy immune system typically has a CD4 count ranging from 500 to 1,200 cells/mm3.
When a CD4 count is lower than 200 cells/mm3, a person will receive a diagnosis of stage 3 HIV, also known as AIDS.
Stage 3 HIV is a separate condition that can develop in a person with an HIV diagnosis. 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 their CD4 levels to typically rise.
What are other factors that affect CD4 count?
HIV is not the only factor affecting CD4 levels.
The
- 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 pneumonia, hepatitis B, or the flu 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
- exercise
- smoking
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 then the body will start to produce antibodies. This can reduce the virus levels.
A viral load can include
Effective treatment will typically result in viral suppression. This is when there are fewer than
As treatment progresses, the viral load can become so low that it’s undetectable in a test. This means there are relatively few copies of HIV in the blood.
When this happens, it is no longer possible for the virus to transfer to another person during sex, according to the
However, continued treatment is necessary to ensure the viral load remains undetectable.
There is a strong correlation between CD4 count and viral load. They have an inverse relationship — as one goes up, the other generally goes down.
In the past, healthcare teams 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 more likely 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.
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.
More frequent testing may be needed if:
- you are just starting treatment
- you change medications
- your viral load is difficult to suppress
| CD4 status | Need for testing |
| Most people with a detectable virus level. | every 3 to 6 months |
| HIV responds well to treatment. CD4 levels have been stable at between 300 and 500 cells/mm3 for 2 years. | every 12 months |
| Viral load remains undetectable. CD4 counts have been over 500 cells/mm3 for 2 years. | may be optional |
However, if any change occurs in the person’s health or treatment status, the healthcare team 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 the HIV.gov website recommend the following intervals for testing:
| Status | Frequency of testing |
| The person has just started antiretroviral treatment, or their healthcare team has changed their treatment. | after 4 to 8 weeks |
| Until the viral load becomes undetectable. | every 4 to 8 weeks |
| While the viral load is stable. | every 3 to 4 months |
Why is it important to get tested regularly?
CD4 and viral load testing can help you and your healthcare team understand:
- how well treatment is working
- your risk of developing an opportunistic infection
- the risk of HIV progressing to stage 3 HIV
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 healthcare professional would need to interpret any results, as they would need to take other factors into account. Healthcare teams also prefer to use the same testing facilities to ensure consistency.
A single CD4 or viral load test result only represents a snapshot in time. It’s important to track both numbers 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.
Blips
Some people may experience blips. These are temporary — often small — increases in viral load. A healthcare team 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 team 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’s body is in a virally suppressed state or has an undetectable viral load, their HIV is well managed.
Effective treatment can also help prevent the transmission of HIV to others. This is also known as “treatment as prevention.”
According to the
No matter the stage of HIV, there are advantages to keeping track of the CD4 count and viral load.
HIV treatment has made significant advances in recent years. Following a recommended treatment plan and leading a health-supporting 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 full life.