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How Accurate Is RT PCR HIV Test?

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Posted on Fri, 21 Feb 2014
Question: How accurate is RT PCR HIV test on 12 th day after a possible exposure. Also i have done HIV Duo Test on 12th day and 29th after the possible exposure. All came negative. Can i take these results to be conclusive that i'm HIV negative.
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Answered by Dr. Dr. Kakkar (1 hour later)
Brief Answer: Very conclusive that you are negative Detailed Answer: Hi Thanks for posting your concern at XXXXXXX The PCR (viral load) is generally not recommended as a diagnostic test; it's used in people who are already known to have HIV to monitor therapy. It shortens the window period to about 17 days (range 13-28 days) days as compared to 3 months in antibody based tests, thus helping in early diagnosis of possible infection (The window period is the time from infection until a test can detect any change). Negative RT PCR Test at 12th day almost rules out HIV infection but i would have been absolutely sure if it was at 15th day or 18th day. HIV DUO test is also known as the 28 day HIV test: This HIV test can detect the virus from 28 days after infection and is called a "Duo" test because it combines an antibody test for the HIV antibody 1 & 2 strains of the virus, with an antigen test for the P 24 antigen. During the first few weeks after someone becomes infected with HIV, only P 24 (Antigen) is detectable in the blood. So the antigen is the first marker of HIV being present. So the HIV DUO test can detect an infection before the antibody test on its own can, it is used for diagnosing HIV much earlier in the course of infection. The test, is considered 99.8% accurate at 28 days, this accuracy increases to 99.9% at 90 days after any potential contact. Therefore a negative result needs to be confirmed with a second test after 90 days, if the exposure is less than 3 months ago** As you mentioned that you did 1st HIV DUO test 12th day after possible exposure and a 2nd one on the 29th day of possible exposure. I would give more reliance to the 2nd test and its negativity almost rules out HIV. The first test that you did was too early after possible exposure. **However since a negative HIV DUO Test result needs to be confirmed with a second test if the exposure is less than 3 months ago, so, I would advice a repeat HIV DUO Test after 3 months of possible exposure to account for the window period (The window period is the time from infection until a test can detect any change). take care regards
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Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
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Dr. Dr. Kakkar

Dermatologist

Practicing since :2002

Answered : 9612 Questions

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How Accurate Is RT PCR HIV Test?

Brief Answer: Very conclusive that you are negative Detailed Answer: Hi Thanks for posting your concern at XXXXXXX The PCR (viral load) is generally not recommended as a diagnostic test; it's used in people who are already known to have HIV to monitor therapy. It shortens the window period to about 17 days (range 13-28 days) days as compared to 3 months in antibody based tests, thus helping in early diagnosis of possible infection (The window period is the time from infection until a test can detect any change). Negative RT PCR Test at 12th day almost rules out HIV infection but i would have been absolutely sure if it was at 15th day or 18th day. HIV DUO test is also known as the 28 day HIV test: This HIV test can detect the virus from 28 days after infection and is called a "Duo" test because it combines an antibody test for the HIV antibody 1 & 2 strains of the virus, with an antigen test for the P 24 antigen. During the first few weeks after someone becomes infected with HIV, only P 24 (Antigen) is detectable in the blood. So the antigen is the first marker of HIV being present. So the HIV DUO test can detect an infection before the antibody test on its own can, it is used for diagnosing HIV much earlier in the course of infection. The test, is considered 99.8% accurate at 28 days, this accuracy increases to 99.9% at 90 days after any potential contact. Therefore a negative result needs to be confirmed with a second test after 90 days, if the exposure is less than 3 months ago** As you mentioned that you did 1st HIV DUO test 12th day after possible exposure and a 2nd one on the 29th day of possible exposure. I would give more reliance to the 2nd test and its negativity almost rules out HIV. The first test that you did was too early after possible exposure. **However since a negative HIV DUO Test result needs to be confirmed with a second test if the exposure is less than 3 months ago, so, I would advice a repeat HIV DUO Test after 3 months of possible exposure to account for the window period (The window period is the time from infection until a test can detect any change). take care regards