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Hiv testing accurate at 21 days as opposed to 28 days?

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I was tested at 21 days post possible exposure with an HIV DNA PCR test that came back negative. The place said they recommend you wait at least 21 days. Now i read that you should wait 28 days to be conclusive. How accurate would the results be at 21 days as opposed to 28 days? and do you feel i need another test or am i safe at the 21 days?
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replied February 29th, 2012
Hello and welcome to e health forum.

First, it is important to know what kind of exposure, you had to determine the need for testing.

HIV DNA PCR is a test, used to detect the presence of Proviral DNA, synthesized from HIV viral RNA, using the reverse transcription technology. it has a sensitivity of 100%. HIV PCR test can be done after 15 days post exposure. The test is indicated only in high risk cases, so that effective therapy can be started at the earliest. In cases where the probability is low, there is no need to do such expensive tests.

In such cases where the PCR is done before 4 weeks, a negative test can reduce initial anxiety and worry, but eventually a HIV antigen / Antibody test should be done to confirm the absence of infection.

In your case, since the HIV DNA test is negative at 21 days, it is highly probable that you do not have HIV. But I would still recommend you to undergo a 4th generation ELISA for HIV, after 4 weeks.

In case, you had a low risk exposure, as determined by your doctor, and the test is negative then it would be certain that you are free from HIV.
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