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The missing percentage points

Question: 

Hello,

I took a rapid 4th generation blood test 5 months post exposure, and I keep reading online that 98% of people will develop antibodies by 3 months (CDC,thebody)

Heres a link: http://www.thebody.com/Forums/AIDS/SafeSex/Q244112.html

It makes me question my result as I want to have 100% confidence in my result, not 98%...the helpline here consistantly states the 4 conditions that delay the result, is there a source so I can read upon it as it would ease my worries. Can I be 100% certain that I am negative?

Answer: 

Hello and thanks for reaching out to the AIDS Vancouver Helpline.

It sounds like you went for an HIV test 5 months post-exposure, your results were negative (I assume), and you want to be 100% sure you can trust your results. Correct? It's definitely understandable to want to be able to have complete faith in the accuracy of your test results. In the link you posted above, a forum poster is wondering whether or not test results are truly conclusive after 6 months. Provided there have been no repeat exposures following the initial exposure, an HIV test done at 6 months post-exposure is considered conclusive by CDC guidelines (you can read more about testing windows at this link here).

Rapid tests look for antibodies that our bodies produce against HIV. The majority of people develop detectable antibodies within 21 to 25 days post-exposure, but in British Columbia, we don't consider test results conclusive until the 12-week post-exposure mark. Given the fact that there are some very rare circumstances in which one's HIV test window may be lengthened (if one is on treatment for hepatitis C, receiving chemotherapy, receiving or has received PEP, or has some other rare immunodeficiency condition), the CDC doesn't consider test results conclusive until 6 months post-exposure. Provided you have not had a repeat exposure since the initial one 5 months prior to your test, you can be very confident in your results. If you want a truly conclusive result, you could consider testing again at the 6 month post-exposure mark, but as has been mentioned, your test result at 5 months post-exposure will be a very strong indicator of your true HIV status.

For more information on window periods and the accuracy of various HIV test results, some good websites are CATIE: HIV Testing Technologies and these HIV Testing Guidelines that we follow here in British Columbia.

I hope this information helps! Thanks again for contacting the AIDS Vancouver Helpline.

Take care,

Erin

AIDS Vancouver Helpline Volunteer

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