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PCR Test Question
      #89868 - 02/20/04 05:21 PM

What exactly is PCR test and where can I get it done? Can it be done annonymously? How reliable is this test? I had heard that it produces a lot of false positives. Is that the case? Please help.

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Reged: 01/27/04
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Re: PCR Test Question new
      #89869 - 02/20/04 05:34 PM

There are tests that can look for the virus – not antibodies – in the blood. Because the virus becomes detectable in the blood much sooner after infection than antibodies, these tests are an option for people who simply can't wait 13 weeks to find out the results of standard ELISA/Western blot testing. And because there has been some encouraging research indicating that people who diagnose their HIV infection early – meaning the first weeks after infection, before antibodies become detectable – can protect their immune systems by starting treatment early, these tests are proving to be very useful for people who recently engaged in a high-risk activity (e.g., receptive anal sex without a condom) and fear they might have been infected.

These tests look for fragments of HIV, either floating around freely in the bloodstream or inside cells in the bloodstream. Some tests – known as qualitative tests – yield a "positive" or "negative" result, meaning that the virus was or wasn't found. Other tests – known as quantitative tests – yield a "viral load" result, meaning the amount of virus in a sample of blood (these quantitative tests are often used to monitor people who are known to be infected with HIV, particularly to find out if their treatment is working properly).

It's important to realize that the FDA has not approved any of these tests for the diagnosis of HIV infection. While they are, indeed, sensitive tests, meaning that they can detect even the tiniest amounts of HIV in a blood sample, they are not always specific, meaning that they can sometimes yield a false-positive result. In other words, if a viral test yields a negative result, it's highly unlikely that you are infected with HIV. However, if the result is positive, it might be a good idea to conduct the test again or to wait 13 weeks for an official diagnosis using ELISA/Western blot.

These tests must be ordered by a healthcare provider, meaning that you should call your doctor if you think you may have recently been exposed to the virus and would like one of these tests. It's also important to keep in mind that these tests can be expensive – between $250 and $400 – and are not usually covered by insurance for diagnostic purposes.

Quantitative Polymerase Chain Reaction (PCR): The quantitative PCR, also known as the viral load test, is considered to be highly reliable for someone who may have recently been exposed to the virus, particularly in a high-risk situation. If the virus is present, the quantitative PCR will reveal how much virus is in a person's bloodstream (the viral load). In most cases, a quantitative PCR is highly accurate within 48 to 72 hours. However, a small number of people don't have viral loads that are high enough to confirm a diagnosis until 28 days after exposure. The most widely available quantitative PCR test, Amplicor® version 1.5, can detect subtypes A through G, which account for 99.96% of HIV infections in the U.S.

The standard recommendation is that a negative PCR result be confirmed with an ELISA test at 13 weeks.

Qualitative PCR: The qualitative PCR, also known as the PCR-DNA test, looks for DNA in cells that suggest that HIV infection has taken place. It is not a viral load test, meaning that it will only determine if the virus is present, not how much virus is present. This test is frequently used to determine if an infant born to an HIV-positive is infected with the virus, given that it can detect virus before viral load becomes detectable. However, it's not at all clear if the qualitative PCR test has any advantages over the quantitative PCR test, which appears to be just as reliable, more widely available, and cheaper to perform.


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Re: PCR Test Question new
      #90664 - 02/26/04 10:25 PM

Jazz how does PCR test differ from the NAT testing you spoke about some posts back? Are there as many false positives? I know blood banks use them. What happens if the antibody test( which is completed first) is neg and NAT is positive? What does the blood bank do in this case? Its obvious that the antibodies will not fly. What do they tell the donor? Are there other tests that the blood bank can do to confirm all of this before the donor is advised??

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