HIV Testing

Section Editor: Rodney E. Rohde PhD
June 2, 2026

HIV testing is used to find out whether a person has been infected with HIV (human immunodeficiency virus). This virus affects the immune system, which is the body’s defense against infection. Testing for HIV is usually done in more than one step, and this is important to understand: a single positive result on the first test is not a diagnosis on its own. Modern HIV tests are very accurate, and HIV is now a treatable, long-term condition.

This article explains the different HIV tests, how they fit together, and what the wording on your report means, so you can better understand a report you have received. It covers both the tests used to find out whether someone has HIV and the tests used to monitor health after a diagnosis.

What is HIV, and why is testing done in steps?

HIV attacks a type of white blood cell called a CD4 cell, which helps coordinate the immune system. Without treatment, HIV can gradually weaken the immune system over time, and the most advanced stage of untreated infection is called AIDS (acquired immunodeficiency syndrome). With effective treatment, this damage can be prevented.

HIV testing is usually done in two stages: a screening test first, then, if needed, a confirmatory test. The screening test is designed to be extremely sensitive so that it catches every possible infection. A side effect of being so sensitive is that the screening test can occasionally be reactive, the word laboratories use for a positive screening result, when there is no true infection. The confirmatory test then determines which reactive results indicate a real infection. This is why a reactive screening result warrants more testing, not a diagnosis by itself.

The screening test

The most common screening test is a blood test that looks for two things at the same time: an antigen and antibodies. An antigen is a piece of the virus itself, and the one this test detects is an HIV protein called p24. Antibodies are proteins that the immune system makes in response to the virus. Because it looks for both, this test is sometimes called an antigen/antibody test or a fourth-generation test.

Looking for both is useful because the p24 antigen appears in the blood earlier than antibodies do. Testing for both, therefore, detects infections sooner after exposure than older antibody-only tests could. Some HIV tests, including rapid tests done with a fingerstick or oral fluid and home self-tests, are also screening tests. A reactive result on any screening test, including a rapid test or a self-test, needs to be confirmed with laboratory testing.

A screening result is usually reported as non-reactive or reactive. A non-reactive (negative) result usually means no HIV infection. However, a follow-up test may be recommended if there was a very recent exposure, given the window period explained below. A reactive result means that further testing is needed to confirm whether HIV is truly present.

Confirmatory testing

When a screening test is reactive, the laboratory performs a different, confirmatory test, usually on the same blood sample. A common confirmatory test is an antibody test that also distinguishes between the two main types of HIV: HIV-1 and HIV-2 (HIV-1 is the most common worldwide).

If this confirmatory test is also positive, HIV is confirmed. If it is negative or unclear, the laboratory usually performs a viral load test, which looks directly for the virus’s genetic material. This step matters because it can detect a very recent infection when the p24 antigen is present, but antibodies have not yet developed. HIV is only diagnosed after this process is complete, and your healthcare provider explains the final result and what it means for you.

The window period

The window period is the time between a possible exposure to HIV and when a test can reliably detect it. During this period, a test can be negative even if a person has been infected, because the body has not yet produced enough antigen or antibodies to be measured. The combined antigen/antibody test shortens the window period compared with older tests, but it does not remove it completely. If a test is done very soon after a possible exposure, it may need to be repeated later to be certain of the result.

Tests used after a diagnosis: viral load and CD4 count

The next two tests are not used to diagnose HIV. They are used to monitor health and guide care after a diagnosis has been made.

Viral load — Measures the amount of HIV genetic material in the blood. It shows how active the virus is and how well treatment is working. The goal of treatment is an undetectable viral load, meaning the amount of virus is too low to be measured. A person who reaches and maintains an undetectable viral load on treatment cannot pass HIV to sexual partners, a fact often summarized as “undetectable equals untransmittable.”
CD4 count — Measures the number of CD4 cells, the immune cells that HIV attacks. It reflects the strength of the immune system. In general, a higher CD4 count means a stronger immune system, and effective treatment helps the CD4 count recover and stay healthy.

How to read your HIV result

The meaning of your result depends on which test was done and where it falls in the testing process.

Non-reactive (negative) screening test — Usually means no HIV infection. A repeat test may be advised if there was a possible recent exposure.
Reactive screening test — A positive result on the first test. This is not a diagnosis. It means confirmatory testing is needed before anything is concluded.
Confirmed positive — HIV has been confirmed through follow-up testing. Your provider will discuss care and treatment with you.
Undetectable viral load — The amount of virus is too low to measure. This is the goal of treatment, and it means the virus cannot be passed to sexual partners.
CD4 count — Reflects the strength of the immune system, with a higher number generally indicating a stronger one.

What happens after an HIV test

An HIV test describes what was found, and it informs the decisions you and your healthcare team make together rather than dictating them on its own. A non-reactive result generally requires no further action, except for a repeat test if a recent exposure is a concern or regular testing if there are ongoing reasons to be tested.

A reactive screening result leads to confirmatory testing before any diagnosis is made, and it is worth waiting for those results before concluding. If HIV is confirmed, it is treated with daily medicines known as antiretroviral therapy. Modern treatment is highly effective. Most people who are diagnosed and begin treatment early can expect a long, healthy life, and effective treatment leads to an undetectable viral load that also prevents them from passing the virus to others. Your healthcare provider, often in collaboration with a specialist, guides treatment over time and can advise on testing and on protecting partners.

Questions to ask your doctor

Which HIV test did I have: a screening test, a confirmatory test, or a monitoring test?
My screening test was reactive. Does that mean I have HIV, or do I need confirmatory testing?
Could it be too soon after a possible exposure for the test to be accurate, and should I be retested?
If my result was non-reactive, do I need a repeat test?
What is my viral load, and what does it tell me about how my treatment is working?
What does “undetectable” mean for my health and for protecting my partners?
What is my CD4 count, and what does it say about my immune system?
If HIV is confirmed, what does treatment involve, and when should it start?
How will my treatment be monitored over time?
Who should I contact with questions about my results or my care?