Factsheet HIV testing

Having an HIV test is the only way to know for sure whether you have HIV. If you have HIV, it’s very important that it’s diagnosed. This will give you the best chance of getting the treatment and care you need to stay well.

Usually, when you go for an HIV test, you will have an opportunity to talk to someone first, so you can ask any questions you might have. The person doing the test will explain how the test works and how you will get the results.

Then, depending on the type of test, you will have a small sample of blood taken from your arm, or a drop of blood taken from your finger. Some tests are performed using fluid from around your gums.

If the test says you are HIV-positive, this means you have HIV. If the test says you are HIV-negative, this means you do not have HIV. With some tests, you will need to have a follow-up test if you have a positive result.

In many countries, including the UK, HIV testing is free and confidential.

HIV tests are available in lots of healthcare settings. This might be in a sexual health clinic, doctor’s surgery, hospital or private clinic, for example. You might be offered a test in other settings, such as in community centres, by trained staff from HIV or community health organisations.

You may also be offered an HIV test as part of care for another health matter, such as antenatal care while you are pregnant, or as part of a sexual health check-up.

In the UK, you can get a free and confidential HIV test at any NHS sexual health or GUM (genitourinary medicine) clinic. These clinics are linked to specialist HIV services, and there will be support available to you if your result is positive.

You can now also test for HIV at home, or take your own sample and then send it to a laboratory for analysis. See NAM’s factsheet Home HIV testing for more information.

Most HIV tests look for one or both of these substances:

• Antibodies to HIV. These are not part of HIV itself, but are produced by the human body as part of its defence against HIV. Antibodies are first produced a few weeks after acquiring HIV.

• p24 antigen, which is part of HIV. There are high levels of p24 antigen in blood a few days before the antibodies are produced. A test for p24 antigen helps diagnose people who have recently acquired HIV.

Laboratory tests are the most accurate. The sample is taken through a needle from a vein in the arm and is then sent away to a laboratory for analysis. It is tested for both antibodies and p24 antigen and you should get the results a few days later. Laboratory tests pick up most cases of HIV within four weeks of it being caught. Occasionally, it may take up to eight weeks for HIV to be detected. Sexual health clinics and hospitals usually use these kinds of tests.

"In many countries, including the UK, HIV testing is free and confidential."

You might also be offered a ‘rapid’ test, using either a small sample of blood from a finger prick or fluid from around your gums. Tests using fluid from around the gums are a little less reliable than ones using blood from a finger prick. The sample doesn’t need to be sent to a laboratory and you will have the result in a few minutes. Many people find these tests more convenient and more comfortable. Rapid tests pick up most cases of HIV within six to eight weeks of it being caught. Occasionally, it may take up to twelve weeks for HIV to be detected.

The vast majority of people get accurate results from rapid tests, but their performance is not quite as good as the laboratory tests described above. Generally, rapid tests only look for antibodies, which means they can’t diagnose people who have very recently acquired HIV. There is one test which looks for both antibodies and p24 antigen, but while it works well in detecting antibodies, its performance in detecting p24 antigen is not as good as laboratory tests.

If a test appears to show that someone has HIV, the accuracy of this will always be verified with a series of extra tests. This ensures that people are not mistakenly told that they have HIV.

If you use a home HIV testing service and the result suggests that you might have HIV, it’s also very important to confirm the result with extra tests. The best place to go is a sexual health clinic, where staff have access to the most accurate HIV testing technologies. See NAM’s factsheet Home HIV testing.