positive).Īll HIV tests need to have reactive results (a preliminary positive result) confirmed with further tests. When using a diagnostic test, the probability that a person who does have a medical condition will receive the correct test result (i.e. This means it is more appropriate to use point-of-care tests in high-prevalence populations, such as with gay and bisexual men, than in the general population. However, as the proportion of people with HIV being tested increases, the true positives start to outnumber false positives. The tests always produce a small number of false positive results, but in a setting where very few people have HIV, the majority of apparent positive results will in fact be incorrect. When used in a population with a low prevalence of HIV, false positive results can be a problem. These include testing at community sites when it is important to avoid a delay in receiving results in situations where it would be difficult to give people their results or if a person does not want to give a venous blood sample. Point-of-care testing is supported is specific scenarios by the British HIV Association (BHIVA) and the National Institute for Health and Care Excellence (NICE). Organisations using point-of-care tests must maintain strong links with a pathology laboratory that provides support with clinical governance and quality assurance. It is good practice for test results to be re-read by a second member of staff, within the time frame specified on the test packaging. In a setting with low prevalence of HIV, staff may not see enough true positive samples to gain experience in interpreting test results. However, reading the test result relies on subjective interpretation, and when the result is borderline, experienced staff give more consistently accurate results. Rapid tests can be performed by staff with limited laboratory training. Other rapid tests, based on older technology, may have longer window periods than this. Fingerprick blood is produced by pricking the finger with a lancet, whereas oral fluid is obtained by swabbing the gums.)Īs a result, the window period of commonly used rapid tests such as the Alere HIV Combo and the INSTI HIV-1/HIV-2 Antibody Test may be one to two weeks longer than for fourth-generation laboratory tests. (Plasma is the colourless fluid part of blood, separated from whole blood using laboratory equipment. Samples of oral fluid have a concentration of antibodies that is lower still. This has a lower concentration of antibodies and p24 than plasma. Point-of-care tests are usually performed on whole blood taken from a fingerprick. Moreover, some can only detect immunoglobulin G (IgG) antibodies, but not immunoglobulin M (IgM) antibodies, which appear sooner. While one antibody/antigen test is available, the other tests look for antibodies only.
The accuracy of point-of-care tests is not always equal to those of laboratory tests, especially in relation to recent infection. Most rapid tests, with the exception of the Alere HIV Combo and Alere Determine HIV-1/2 cannot detect p24 antigen. In contrast, the recommended laboratory tests also detect p24 antigen, a protein contained in HIV's viral core that can be detected sooner than antibodies. The latest news and research on types of HIV tests In the weeks after exposure to HIV, the immune system recognises some components of the virus and begins to generate HIV antibodies in order to damage, neutralise or kill it (this period is known as ‘seroconversion’). They are not part of HIV itself, but are produced by the human body in response to HIV infection. They are called ‘rapid’ tests because the result can usually be given within a few minutes. Other tests require oral fluid (an absorbent pad is swabbed around the outer gums, adjacent to the teeth). Most point-of-care tests require a tiny sample of blood (the fingertip is pricked with a lancet). Rapid tests are often referred to as point-of-care tests because rather than sending a blood sample to a laboratory, the test can be conducted and the result read in a doctor’s office or a community setting, without specialised laboratory equipment. Like any screening test, a reactive (‘positive’) result must be confirmed with one or two follow-up tests.Many tests are based on older ‘second-generation’ technology, but a ‘fourth-generation’ test with better performance is available.Rapid tests are usually reliable for long-standing infections, but are sometimes unable to detect recent HIV infections acquired in the past few weeks.
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