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 Sir, I recently had an unprotected sex with a commercial sex worker on 4/12/2012. I went for a H1 , H2 antibody & P24 antigen test on 28/12/2011 which is exactly on 24th day of unprotected exposure. I have heard that test on 28th day gives 95% accuracy. So what is the accuracy level of the test on 24th day ? I will obviously go for another test on 6th week and 3 months. thanks.


Hi and thank you for using the AIDS Vancouver Helpline as a resource for your inquiries.
First of all, congratulations for being very responsible by getting tested for HIV- at the end of the day, testing is the only way to know for sure.
The 4th Generation EIA (aka Duo or Combo) Test looks for both antibodies and P24 protein antigens. The antigen portion of the test is detectable immediately after infection (3-4 days), for the first 2 to 4 weeks. The antibody portion of the test is typically detectable from 4-6 weeks onward. Many HIV specialists consider this test to be conclusive at 6 weeks. So, your test at 28 days is a very good indicator of your status, regardless of the type of exposure or those statistics for vaginal sex risk you quoted.
Your email does not provide me with you location however, in Canada testing guidelines recommend re-testing at 3 months.
Unfortunately, no test for anything will be 100% but we take accuracy of 99.9% for a 4th Generation EIA at 12 weeks/3 months as conclusive.
Once you are retested at 3 months and if you have had no further risky encounters (unprotected anal or vaginal intercourse), you can rest assured that you are negative. We also highly recommend you to be tested for other Sexually Transmitted Infections (STI's), as there is a very high risk of contracting one or more of these infections through many different types of sexual contact.
I trust I have addressed all of your concerns. However, should you have further questions, please feel free to contact us again.
Stay safe and healthy!
AIDS Vancouver Helpline Volunteer
604.696.4666, Monday-Friday, 9AM-4PM PST