Tests, tests, tests

What are the reasons to get tested for HIV?

            There are a number of important reasons to be tested for HIV. The longer a person remains unaware of their infection, the less likely it is that the treatment will work. By knowing your status, you can find out whether or not you can infect others, and what precautions you might take to prevent transmission to other people.

What Are HIV Antibody Tests?

            As the body fights viruses, the immune system creates antibodies to that virus. HIV antibody tests do not measure or detect the virus itself. If antibodies to HIV are detected, it means a person has been infected with HIV. There are only two exceptions to this rule:
    =Babies born to HIV infected mothers retain their mother's antibodies for up to 18 months, which means they may test positive on an HIV antibody test, even if they are actually HIV negative. Normally babies who are born to HIV positive mothers receive a PCR test.
    =Some people who have taken part in HIV vaccine trials may have HIV antibodies.

            With this test, an initial assay is used (the ELISA), and confirmed using a more specific test (the Western Blot).

Rapid tests

            These tests are based on the same technology, but instead of sending the sample to a laboratory to be analysed, the rapid test can produce results within 20 minutes. Rapid tests can use either a blood sample or oral fluids. They are easy to use and do not require laboratory facilities or highly trained staff.
            All positive results from a rapid test must be followed up with a confirmatory test, the results of which can take from a few days to a few weeks.

What is a window period?

            The "window period" is the time it takes for a person who has been infected with HIV to react to the virus by creating HIV antibodies. This is called seroconversion.
            During the window period, people infected with HIV have no antibodies in their blood that can be detected by an HIV test, even though the person may already have high levels of HIV in their blood, sexual fluids, or breast milk.
            The three month window period is normal for most of the population. Many people will have detectable antibodies in three or four weeks. Very, very rarely, a person could take six months to produce antibodies.
            It is very important to note that if a person is infected with HIV, they can still transmit the virus to others during the window period.

Western Blot (WB)

            The WB is a confirmatory test. It is only performed if an ELISA or rapid test is positive. The WB can be positive, negative, or indeterminate. An indeterminate result usually means that a person has just begun to seroconvert at the time of their test. In the rare cases in which this occurs, the person will need to be retested, usually about one month later. False positive results are extremely rare with the WB, so it confirms that HIV antibodies are present.

Antigen test

            Antigens are the substances hat trigger the production of antibodies in the body. The antigen on HIV that most commonly provokes an antibody response is the protein P24. Levels of p24 antigen increase significantly at about one to three weeks after initial infection. It is during this time frame before HIV antibody is produced when the p24 test is useful in helping to diagnose infection.

Fourth generation tests

            Some of the most modern HIV tests combine P24 antigen tests with standard antibody tests to reduce the ‘diagnostic window’. Testing for antibodies and P24 antigen simultaneously has the advantage of enabling earlier and more accurate HIV detection.

PCR test

            A PCR test (Polymerase Chain Reaction test) can detect the genetic material of HIV rather than the antibodies to the virus, and so can identify HIV in the blood within two or three weeks of infection. The test is also known as a viral load test and HIV NAAT (nucleic acid amplification testing).
Babies born to HIV positive mothers are usually tested using a PCR test because they retain their mother's antibodies for several months, making an antibody test inaccurate.

If you are interested, here is a list of places where you can be tested for free. link

Sources:
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avert.org
wikipedia.org
thebody.com
labtestsonline.org