An undetectable viral load describes when there is so little HIV in the blood that a test cannot detect it. If HIV is undetectable over an extended period, it is also untransmittable.

Although having an undetectable viral load does not mean that a person no longer has HIV, it offers tremendous promise for a person’s overall health and reduces viral transmission.

In this article, learn more about what having an undetectable viral load means, as well as how healthcare professionals test for it.

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A viral load test measures the number of viral copies of HIV in a person’s blood. Typically, the higher a person’s viral load, the greater their chance of transmitting HIV.

However, antiretroviral therapy can reduce the number of viral copies in a person’s blood to levels that are so low that they do not register on a viral load blood test. Healthcare professionals call this an undetectable viral load.

Although the measurement for an undetectable viral load can vary by laboratory, it is usually fewer than 40 copies per milliliter (ml).

A healthcare professional may also use other terms related to an undetectable viral load, such as durably undetectable or viral load suppression.

When a person’s viral load has been at undetectable levels for 6 months or longer, it is durably undetectable.

Viral load suppression means that a person’s viral load is fewer than 200 copies per ml. Although the virus is not undetectable, people with a viral load this low will not transmit the virus.

An undetectable viral load is an important milestone for a person living with HIV because it signifies that the amount of the virus in their body is less likely to cause health problems.

Several long-term landmark studies into the effects of antiretroviral therapy on HIV have led researchers to conclude that having undetectable levels of HIV means that the virus is untransmittable.

In one study, researchers enrolled 1,166 couples who had vaginal or anal sex without a condom. In each couple, one partner had HIV, had viral suppression, and was undergoing antiretroviral therapy.

The researchers studied them for an average of 1 year and 4 months per couple. In the follow-up period, there were no instances of HIV transmission within the couples.

A study that researchers presented at the 2017 International AIDS Society conference came to similar conclusions. The study’s authors recruited 358 sex-same male couples in Australia, Thailand, and Brazil.

In each couple, one partner had viral suppression, was undergoing antiretroviral therapy, and had HIV. At the study’s conclusion, the researchers found no evidence of HIV transmission between partners after sex without a condom.

Results from these and other studies have led many large organizations, including the Centers for Disease Control and Prevention (CDC) and the United Nations, to concur that having undetectable viral levels means that HIV is untransmittable via sex. This is known as undetectable = untransmittable, or U=U.

Several types of tests exist for HIV. For example, there are tests to determine to what extent HIV affects the body, such as CD4 count, which assesses how HIV has affected a person’s immune system.

Healthcare professionals are using these tests less in people undergoing antiretroviral therapy, but they remain the best measurement of a person’s immune and clinical status.

Doctors use viral load tests to determine whether a person has viral suppression or has undetectable HIV levels. These tests measure the amount of HIV RNA molecules in the blood.

A healthcare professional can discuss which test they will use and what the results mean based on the laboratory’s standards.

A person who is taking antiretroviral medications and who has a stable viral load will usually undergo these tests every 3 to 4 months. If a person has had viral suppression for longer than 2 years, they may only need to have their viral load tested every 6 months.

Other tests, such as rapid tests, can screen for HIV. They use a small sample of blood or saliva to detect the presence of antibodies to HIV.

According to UNAIDS, an estimated 47% of those who have HIV have virally suppressed it. The fact that antiretroviral therapy can improve people’s health and reduce transmission of the virus has the power to help millions of people around the world.

A variety of antiretroviral medications exist. A healthcare professional should discuss the options and possible combinations with a person. They will consider the stage of HIV the person has, the person’s overall health, potential treatment costs, and many other factors when recommending a treatment course.

Typically, a person who has recently received an HIV diagnosis will take at least three antiretroviral medications in response to the virus. These medications keep HIV from replicating. Having less HIV in the body gives a person’s immune system an opportunity to manage the virus.

A person will not immediately develop viral suppression when they start taking antiretroviral medications. It may take 6 months or longer before the viral load reduces, so it is vital that people start treatment as soon as possible.

Continuing to take antiretroviral therapy is crucial to ensure that HIV remains untransmittable. Even with an undetectable viral load, the virus is still present in the body.

If a person stops taking antiretroviral therapy, the virus may begin to multiply again.

If a person living with HIV has an undetectable viral load for 6 months or longer, the virus is untransmittable. Having an undetectable viral load also drastically reduces the chance of HIV causing any additional health problems.

Consistently taking antiretroviral medications can bring a person’s HIV levels down to an undetectable level.

If a person has recently received an HIV diagnosis, they should work with a healthcare professional to begin a treatment plan as soon as possible.