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How does the doctor test my blood or saliva for HIV?


Updated May 16, 2014

Question: How does the doctor test my blood or saliva for HIV?
Testing for HIV is done in two stages. First, a primary test is done. If it is positive, then the test is repeated to check for false positives. If the primary test is positive twice, then the sample is tested with a second, more specific, confirmatory test to make certain that the primary test isn't reacting to an infection other than HIV.

The types of test include:

  • Primary Tests
    • EIA – Enzyme Immune Assay – Tests for antibodies to HIV. Although most people start producing anti-HIV antibodies within 6-12 weeks of infection, it can take up to 6 months for your body to produce enough antibodies to test positive on an EIA test. Therefore this test is not useful for newly infected individuals. If you have recently been infected with HIV, you may not test positive, but that does not mean you can’t still pass the virus on to other people.
    • ELISA – Enzyme Linked Immunosorbent Assay- Similar to the EIA.
    • PCR – Polymerase Chain Reaction – This test uses technology to amplify viral RNA from the blood, and it can detect even small amounts of virus in a newly infected person. However, it is expensive, time consuming, and not readily available

  • Confirmatory Tests
    • Western Blot – The main method used to confirm the results of an initially positive test. It is an antibody test that is more specific for HIV-antibodies than the EIA/ELISA tests. However, it is substantially more expensive which is why it is used for confirmation instead of initial testing.
    • RIPA- A blood test done when antibody levels are low or the Western Blot results are unclear. This test is expensive, difficult to perform, and not often used.
    • Immunofluorescence Assay – Another type of confirmatory test used when Western Blot results are unclear. Sometimes used instead of a Western Blot after an ELISA test.
    • DNA/RNA Amplification Tests – Tests similar to PCR that are occasionally used when the result of a western blot is unclear.
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