Jul 26, 2006
What is a PCR test? How accurate is it and after how long can it be considerd conclusive and why is it not available easily?
Response from Dr. Conway
The PCR test is used to detect HIV itself (usually in the plasma or circulating blood cells) rather than an antibody response to it. The approved clinical test for the diagnosis of HIV infection is a screening ELISA test with a confirmatory test, usually a Western blot. If both are positive, then a diagnosis of HIV infection can be made. This is a conclusive result unless you suspect that someone has been infected in the previous 3-6 months. In that type of situation, it may be that the test is falsely negsative because antibodies have not yet developed. In that setting, a PCR test can be done to see if the virus itself is present. If the test is negative, this is reassuring byt the only test that can be considered conclusive to rule out the presence of HIV infection is the antibody test result performed 3 months after a possible exposure. So, it is not that the PCR test is ntot easily available (although it is much more expensive than the antibody test), it is just not often needed as a diagnostic test. When it is needed, it is fairly widely available, speaking of developed countries.
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