Here’s why you test positive for HIV if you’re undetectable

If you’re undetectable, you will still test positive for HIV. This is expected, and doesn’t mean that your treatment is not working.

Every year, San Francisco AIDS Foundation conducts more than 15,000 HIV tests. People from all over the Bay Area—even all over the world—access our services find out their HIV status. Only a very small percentage of the tests we run come back positive, and we know how to provide people who are newly diagnosed with the support, resources and care to continue living healthy lives. We’re puzzled however, when we find out clients are seeking our HIV testing services when they’re HIV-positive, and are sometimes even in care and taking HIV medications.

What’s going on?

Why might people living with HIV get tested for HIV?

Because we connect with every single person who tests positive at one of our locations, we always ask why people get tested for HIV if they’ve already been diagnosed in the past.

It happens for many reasons: People may test with a partner they haven’t yet disclosed to, they may have mental health concerns that come into play, or they need a letter of diagnosis to access services (such as a shelter bed). Sometimes it’s because they are confused about the kind of information an HIV test will provide.

Now that we know undetectable equals untransmittable (U=U), some people may have the misconception that if you’re undetectable, you will no longer test positive for HIV. They may think that if they test HIV-negative on an HIV test, they’ll be able to show this to their sex partners as a way to “prove” that they’re undetectable and untransmittable. Or, they may think it will be easier to tell partners they’re HIV-negative rather than undetectable and uninfectious.

If you are living with HIV and have an undetectable viral load, you will still test positive for HIV. But, if you are living with HIV, have been taking HIV medications every day as directed, have a “durably” suppressed viral load and have been undetectable for at least six months, you will not transmit HIV to sex partners. You are not infectious. That’s the meaning of U=U.

Here’s why you will still test positive for HIV even if you are undetectable.

Testing positive on HIV antibody tests 

Since the early days of the HIV epidemic, we have used antibody tests to test for HIV. (In the past, HIV testing was done typically done first with an ELISA or screening test, which was confirmed by a western blot assay identifying specific antibodies. Newer tests often combine an antibody test with an antigen or protein assay which provides more sensitivity for early infection.) Antibody tests are the most affordable and accessible HIV tests. They are the most common types of HIV tests at testing sites around the world because they provide rapid, on-the-spot results.

Antibody tests do not detect HIV. Instead, they detect antibodies that the immune system produces in response to HIV infection.

Want to know more about different types of HIV tests, how they work and how early they detect HIV? Check out this easy-to-read guide from Avert or read this Q&A by the CDC.


Our immune systems develop antibodies in response to all kinds of pathogens. Anytime you get sick or get any kind of infection, your body builds up a defense system and creates antibodies to try and fight that specific infection off. If these antibodies are successful, some infections will go away but the antibodies never do. They will remain in your body, helping to protect you from getting the same infection in the future.

In this way, antibodies allow our bodies to “remember” a specific infectious agent—like a particular strain of the flu—and then respond to it more quickly if exposed to it again in the future. Once we develop antibodies to a virus (or in response to a vaccine) we may have those antibodies for life or for many years.


Unfortunately, the HIV antibodies generally do not help much in terms of fighting off the infection or preventing it. But once we develop an HIV infection and develop HIV antibodies, those antibodies stick around for many years.


Antibodies are still present in individuals living with HIV—even people who have suppressed their viral load. That means people living with HIV will still test positive for HIV on an antibody HIV test even if their viral load is undetectable. The virus may be undetectable, but antibodies are still present and detectable.

Keith Henry, MD, an HIV specialist at Hennepin County Medical Center explained that even if people living with HIV were being cured—so that they no longer had any viral material in their body—many people who were cured would still test HIV-antibody positive. The antibodies would be sort of a “historical marker” from a past HIV infection.

Testing positive on nucleic acid tests 

In addition to antibody tests, we also have HIV tests that detect viral RNA —not necessarily live virus, but parts of the virus’ genetic material. These are called nucleic acid tests, and they are able to detect very early HIV infections. These tests are not used as often for screening as antibody tests (or antibody/antigen tests), because results take longer and the test is more expensive. Usually, RNA tests are used to confirm an HIV positive diagnosis after someone tests positive on an antibody test or to see if a person is responding well to treatment.

Some of these viral detection tests are able to detect virus at very low levels. Some research HIV RNA assays (called ultrasensitive tests) can measure HIV RNA levels down to the single copy levels.

We commonly say someone is “undetectable” if they have a viral load less than 20 copies/mL or 50 copies/mL. Research studies have defined “undetectable” as any viral load less than 200 copies/mL.

So even if a person has a viral load less than 50 copies/mL or 20 copies/mL, viral RNA will still be detected with one of these viral detection tests.

“Detecting a very small amount of virus on one of these tests shows that a person is not cured,” said Henry. “But it has no practical clinical meaning while you’re on effective therapy based on our current understanding. By all clinical standards, if you are under 50 copies, that is what matters. Having an HIV RNA level less than 25, versus less than 50, for instance, doesn’t mean anything clinically as far as current management or transmission risk assessment is concerned.”

A viral load test will let you know if you are undetectable 

If you’re living with HIV and want to know if you’re undetectable, the right test for you is called an HIV viral load test. Similar to nucleic acid tests to detect HIV infection, HIV viral load tests measure the number of copies of HIV in a milliliter of your blood. It’s recommended that people living with HIV get HIV viral load tests generally every 3 to 6 months, in addition to other lab tests that measure your CD4 count and more.

The bottom line is that if you’re living with HIV and have an undetectable viral load, you will still test positive for HIV if you get tested. But, this is expected, and doesn’t mean that your treatment is not working or that you aren’t undetectable. As always, check with your HIV care provider if you have questions about what HIV test is right for you, or what types of tests will give you the answers you need to best care for your health.

San Francisco AIDS Foundation offers a variety of free, confidential sexual health services including HIV and STI testing, linkage to HIV care, PrEP and more.