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This indicates that half of all infections would be detected between 13 and 24 days after exposure. The median window period is 18 days (interquartile range 13 to 24 days).Commonly used tests of this type include Abbott Architect HIV Ag/Ab, GS Combo Ag/Ab EIA and Siemens Combo HIV Ag-Ab. It uses a sample of blood plasma or serum and can detect immunoglobulin G (IgG) antibodies, immunoglobulin M (IgM) antibodies and p24 viral antigen (a protein contained in HIV's viral core that can be detected sooner than antibodies). Moreover, their data suggest that some countries’ guidelines which recommend retesting 90 days after a possible exposure to HIV are more cautious than they need to be.Ī fourth-generation laboratory testis recommended in UK and US guidelines.

The researchers’ analysis confirms that fourth-generation laboratory tests (which detect both antibodies and p24 antigen) detect HIV infections between one and three weeks earlier than older antibody-only tests. NAM aidsmap's Matthew Hodson explains about window periods for HIV testing. Unfortunately, precise figures for how much longer the window periods are have not yet been published. Window periods are likely to be several days longer when testing samples of fingerprick blood or of oral fluid, as will be normal when using rapid, point-of-care tests and self-testing devices. All these analyses were based on plasma samples. Nonetheless, a study by Dr Kevin Delaney and colleagues calculated window periods for a range of HIV testing assays. It is hard to say exactly how long the window period lasts, as there are variations between individuals and it is a difficult topic to research (recently infected people would need to know exactly when they were exposed to HIV and then give multiple blood samples over the following days and weeks). How long are the window periods of different HIV tests? At this stage, it is highly likely that a negative result is accurate. The information given in UK testing guidelines about window periods is based on answers to the second question – specifically, how long after exposure to HIV 99% of infections will be detected by a specific type of test. How soon after exposure to HIV can an individual be confident that a negative test indicates they do not have HIV?.How soon after someone is exposed to HIV can the test detect whether they have HIV? (Some, but not all, infections may be detected at this stage).There are two key questions to ask about a specific HIV test: The latest news and research on types of HIV tests Fingerprick blood is produced by pricking the finger with a lancet, whereas oral fluid is obtained by swabbing the gums.) (Plasma is the colourless fluid part of blood, separated from whole blood using laboratory equipment. It also depends on the specimen that is being tested: window periods are usually reported based on a sample of blood plasma, but are longer when the specimen tested is fingerprick blood or oral fluid. Tests cannot always detect HIV infection during the window period.Īll tests have a window period, which varies from test to test.

The window period refers to the time after infection and before seroconversion, during which markers of infection (p24 antigen and antibodies) are still absent or too scarce to be detectable. The window period of rapid, point-of-care tests and self-tests is 90 days.