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Is rNA PCR test for HIV accurate at 18 days post exposure?

can anybody please tell me if rNA PCT test for HIV gives accurate results 18 days after suspected exposure? i know the test is expensive but i can afford it. also mention the source of your information.

There is nothing better than the standard HIV antibody blood tests for the diagnosis of HIV infection (ELISA/WEstern Blot). It really still is the gold standard for HIV screening with an 99.7% sensitivit and a >99.9% specificity. You can't get much better than that.

That being said, an HIV RNA PCR test (which I am assuming is what you are talking about) has a false positive rate of 2-9% almost always showing low level HIV viral load (<10,000 copies/ml). The sensitivity of this test depends on viral load (amount of circulating virus in the blood), threshold of various assays, and whether or not the patient is on antiretrovirals. Sensitivity does approach 100% in patients with acute/early HIV infection, specificity is 97% (more with higher viral loads). This test can be useful in the diagnosis of acute HIV infection, but should not be used in lieu of the standard HIV serology I mentioned initially.

My advice to you is to test using the standard HIV serology. You can test at 20 days post infection (knowing that 75% of people would test positive by then if they were infected) and test again at 3 months for a definitive result. By the time the HIV RNA PCR test is taken, analyzed, and results are available and with the possibility of having to redo the test, or have to do the standard HIV serology after the PCR makes sense to just do the standard HIV antibody tests.

The HIV RNA PCR test is used for a variety of reasons, many of which occur after someone has completed the standard serology and there are still questions about the result.

Hope this helps

Karan S,
There is an HIV test referred to as ELISA (enzyme-linked immunosorbent assay) or, alternatively, EIA (enzyme immunoassay), these tests detect HIV antibodies, which the body starts producing between 2 and 12 weeks after becoming infected with HIV. This is why experts recommend that you wait to take an antibody test until 3 months (12 weeks) after an incident (such as unprotected sex) that may have led to HIV infection. This recommendation may be changing, as the latest generation of tests is more sensitive than previous ones and can detect HIV antibodies about 2 to 6 weeks after infection. Using technology similar to that of an ELISA, a rapid test, which appears to be the test that you are quoting, produces results in approximately 20 minutes. Two types of rapid tests are available now. One uses blood; in this case, a clinician pricks your finger with a small needle and takes a few drops of your blood. The other uses oral fluids and is very similar to the oral fluid test described above. There are two possible outcomes with this test 鈥?鈥淣egative鈥?(meaning that the test does not detect any HIV antibodies) or "preliminary positive." In the case of preliminary positive, the rapid HIV test shows an HIV-positive result, but, as with the ELISA test, that result must be confirmed with a second test such as a Western blot. If the result is preliminary positive, the counsellor will discuss what this means with the client, including the importance of practicing safer sex and taking other precautions until the confirmation test results come back, and will schedule a time for the client to receive confirmatory results and additional counselling. I shall not get into the area of discussing confirmation tests, viral load or the like at this stage.


The information provided here should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions.

I add a Wikipedia link with details of this subject

Hope this helps
matador 89

In truth, none of these tests are ever likely to be 100%. They have had cases of dormant STD infections that went tested and undetected for years, even up to 10 years has been documented. If your immune system is healthy enough to tuck the infection away and prevent it from spreading for a while, it will. This prevents anything from showing up on many tests until the immune system gets low for some reason and allows an outbreak or the virus. This is most common with HPV where women usually go several years without it showing up on tests. HIV is the same, and it is usually recommended to continue testing for years to be sure, if you think you could have been exposed.

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