Diagnostic tests for HIV are sometimes used to identify how recent or established an infection is, however the main goal of using these tests is to detect HIV infection early on (Iweala, 2004). This can be done by using samples of blood, saliva or urine to test for antibodies or antigens linked with HIV infection (Mandell et al., 2009).
A sample of blood in some form is used for several of the HIV diagnostic tests (Iweala, 2004). From this sample it is possible to identify whether there is HIV infection and what type of viral (HIV-1 or HIV-2) infection it is. The amount of viral particles in the blood (viral load) can also be determined from the sample as well as when the viral infection was contracted and whether there is resistance to HIV drugs (Iweala, 2004).
If there are no HIV antibodies present in the blood then the individual may be described as 'seronegative' or 'HIV-negative'. However, if a person is found to have evidence of HIV infection they may be considered 'HIV-positive' (Iweala, 2004). It takes a few months before HIV antibodies can be made and therefore a person may present as 'seronegative', while still being 'HIV positive'.
Blood may be collected from a vein or by a finger prick, though there are other options including providing saliva or urine samples for the tests (Iweala, 2004). The diagnostic tests that use saliva or urine may be as reliable in giving a correct result as the tests that use blood samples if done at the right time, but they don’t allow as much investigation into the infection as the blood samples do (Mandell et al. 2009).
HIV Diagnostic Tests
1. Enzyme Linked Immunosorbent Assay (ELISA) and Western Blot
The ELISA test and Western Blot are the most common tests for HIV and are used to detect whether the person has proteins that fight HIV (HIV antibodies) (Iweala, 2004). The ELISA test is done first (Porth, 2005) and if it shows positive then the Western Blot assay is also done. Most often these tests can accurately detect the presence of HIV antibodies. However if the tests are done during the "window period" (before sercoconversion has taken place), a false negative test is possible (Mandell et al. 2009). For this reason, negative tests usually require a follow up test 3 months later (Fahey & Flemming, 1997).
2. Detuned Assay
This test gives an indication of how recent the HIV infection is (Mandell et al. 2009). Iweala (2004) explains that a second test is done on the sample of a person who has a positive result using the ELISA test and if the HIV infection is recent (within 129-180 days) the test result for the detuned assay will be negative. This is an important test because it can show new infections and how prevalent HIV infection is for the general public (Iweala, 2004).
3. Urine and Salivary Tests
These tests are used to concentrate specific antibodies for the ELISA and Western blot tests (Mandell et al., 2009). An example of an approved oral test is the Orasure test which is sold over the counter (Porth, 2005).
4. Rapid Tests
Rapid tests don’t require highly trained people to do them; the results are comparably reliable to ELISA and Western Blot test results (if there isn’t a high risk of acute HIV infection) and may be produced within an hour (Iweala, 2004, Mandell et al., 2009, Pascoe et al., 2009).
Additional Tests
1. HIV nucleic acid-based assays
According to Iweala (2004) this test is used after a person has been confirmed to have an HIV infection to find out the viral load. The viral load can then be used as an indication of how effective the medication is for the person as well as the development and likely timeline of the infection (Mandell et al., 2009).
2. p24 antigen detection
This type of test is not used often but when it is used it gives an indication of the levels of a specific antigen in the sample and can be used to clarify results from a Western blot test.
3. Peripheral blood mononuclear cell culture
This test takes places over a period of at least 28 days and can be used to detect HIV infection in infants. However, it is expensive and used in predominantly in research settings (Iweala, 2004).
Testing should be done for all pregant women and regularly for any individual who is at risk of contracting HIV. (For more information on HIV risk factors click here)
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