What to Know About Your CD4 Count and Viral Load

If an HIV infection has been confirmed, tests are routinely performed to determine the status of a person's immune system and the level of viral activity in the body. These are expressed in what is known as your CD4 count and viral load.

Vials of blood to be tested.
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What Is a CD4 Count?

The CD4 test is one of the more familiar testing assays known to people with HIV. The test measures the level of CD4 helper T-cells in the blood—cells that are not only vital to immune function but are the primary target of HIV infection. As HIV gradually depletes these cells, the body becomes less able to defend itself against a widening range of opportunistic infections.

The test is performed by taking a blood sample, the results of which measure the number of CD4 cells in a microliter (µL) of blood. The baseline count establishes the status of your immune system, while follow-up testing largely informs us about:

  • The stage of infection and rate of disease progression
  • The likelihood that certain infections will develop as CD4 cells are depleted
  • How well you are responding to treatment either by maintaining or reconstituting your immune function

Normal CD4 counts are anywhere between 500-1,500 cells/ µL. Conversely, a CD4 count of 200 cells/ µL or less is technically classified as AIDS.

Previous treatment guidelines recommended that antiretroviral therapy (ART) be initiated in patients with a CD4 count under 500 cells/µL or in the presence of an AIDS-defining illness. In 2016, updated guidelines from the World Health Organization endorsed ART in all HIV-infected patients, irrespective of CD4 count, location, income, or stage of disease.

Today, the CD4 count is used to predict disease outcome as much as to measure an individual's relative immune strength. By way of example, the CD4 nadir (the lowest point to which the CD4 count has dropped) is predictive of long-term morbidity, with lower values suggesting an increased risk of HIV-related and non-HIV-related illnesses, as well as slower immune recovery.

What Is a Viral Load?

While the CD4 count is an indicator of immune status and treatment efficacy, the viral load is arguably the more important measure when antiretroviral therapy begins.

The viral load measures the concentration of virus in the blood, also known as your "viral burden." Labs will use a genetic testing technology—typically, the polymerase chain reaction (PCR) or a bDNA (branched DNA)—to quantify the number of viral particles in a milliliter (mL) of blood. HIV viral loads can range from undetectable (below the detection levels of current testing assays) to the tens of millions.

An undetectable result does not mean there is no virus in your blood or you have been "cleared" of infection. Undetectable simply means that the virus population has fallen below testing detection levels in blood but may be detectable elsewhere, such as in the semen.

Goals of Viral Suppression

The aim of antiretroviral therapy is to achieve viral suppression, defined as having fewer than 200 copies of HIV per millilter of blood.

  • Greater treatment durability
  • A lower risk for the development of drug-resistant virus
  • Better clinical outcomes correlating to increased life expectancy
  • The reduction of HIV transmission to no risk to an uninfected sexual partner (a strategy popularly referred to as treatment as prevention (TasP)

On the other hand, an increase in the viral load can often be an indication of treatment failure, poor drug adherence, or both.

It's important to note that drug adherence of at least 80% to 85% is required to ensure viral suppression to undetectable levels. Uneven adherence not only reduces a person's ability to achieve this, it increases the likelihood of treatment failure by allowing a drug-resistant virus to develop. This cause-effect relationship is the reason adherence should always be checked before therapy is changed.

That said, incidental variations in viral load (or "blips") can occur even among those with 100% adherence. These are usually minimal and should not be the cause for alarm.

Regular monitoring of the CD4 count and viral load is recommended. Patients able to sustain CD4 counts over 500 cells/µL may be tested occasionally as directed by treating doctor.

Benefits of Viral Control

According to research from the U.K. Collaborative Cohort Study (UK CHIC), people with undetectable viral loads who achieved a CD4 count of 350 cells/µL or more within a year of starting therapy were likely to have a normal life expectancy.

On the flip side, failure to achieve viral suppression reduced life expectancy by as much as 11 years.

A 2013 retrospective study conducted at the University of Montreal monitored 1,357 HIV-positive men from 1999 to 2011, further demonstrated a virologic failure rate of nearly 60% in persons with persistent viral loads of between 500 and 999 copies/mL.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Lamp K, McGovern S, Fong Y, et al. Proportions of CD4 test results indicating advanced HIV disease remain consistently high at primary health care facilities across four high HIV burden countriesPLoS One. 2020;15(1):e0226987. doi:10.1371/journal.pone.0226987

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  4. National Institute of Allergy and Infectious Diseases. 10 things to know about HIV suppression.

  5. CDC. HIV Treatment as Prevention.

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Additional Reading

By James Myhre & Dennis Sifris, MD
Dennis Sifris, MD, is an HIV specialist and Medical Director of LifeSense Disease Management. James Myhre is an American journalist and HIV educator.