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How are window periods proved?

Question: 

Hi, there.

I tested 4th generation test for 4, 6, 8 weeks after I had exposure with Thailand sex worker, and it was negative.
Also, I tried to confirm myself to have a last test at 12 weeks with oraquick, and it was negative.

So, as far as I know, I am negatvie and there shouln't be any more doubt about it.
But since my girlfriend was having fever and throat pain for few days, I started to worry about hiv again...

My biggest question is that, how we can really confirm that window period is 12 weeks(or 3month)?
I found that, it is really difficult to find someone who found out themselves about their hiv infection in 12 weeks, as i see, most of them didn't even know if they had it, and just diagnosed few months, or even few years later.

So how these doctors figured out that window period is 12 weeks? and also, as you may know, Hiv-2 is really really rare in everywhere except for West Africa, then how they could find out hiv-2 window period?

please give me answers..I am still worried..
sorry for my poor english.

Answer: 

Hello,

Thank you for your inquiry. From what we gather from the question, you were asking about how the window periods for HIV tests are determined and proved.

Window periods are estimations based on the the time between when a person becomes infected with HIV to when a test can accurately detect the infection (1). The following is a direct quote from a presentation given by a BCCDC Doctor: 'Window periods are not absolute. They are determined from models, averages or estimates based on studies of a small number of seroconverting individuals, typically among repeat blood donors`(2). Based off of this information window periods for different tests are created. For example, 4th Generation tests (HIV Ag/Ab Test) can detect HIV infections in 50% of people 18 days post-infection, 95% of people 34 days post-infection, and 99% of people a 6 weeks post-infection (1). Since 99% of people are accurately diagnosed after 6 weeks the test is said to be conclusive my most HIV specialists, and it is thus outside the "testing window". For completely conclusive results, some physicians and guidelines recommend re-testing after 12 weeks in which the 4th Generation test will be 99.9% conclusive.

Any test that is not conducted in the laboratory, such as OraQuick for at home testing, has a larger margin of error than tests conducted by laboratory professionals (1). In your case, a negative OraQuick result at 12 weeks is likely to be accurate due to your previous testing history, but a 4th Generation Test (which test for antigens against HIV-1 and antibodies against both HIV-1 and HIV-2) would be the most accurate in providing a conclusive negative result at this time.

Recommendation: Refer to a physician for a 4th Generation Test and any other health related questions.

Regards, AIDS Vancouver Helpline/Online, Marie