I'm going to stop by the blood bank tomorrow and check on the current state of HIV testing.yovargas wrote:The regular HIV test does not detect the virus but the antibodies that the body produces in response to the virus. The test has a certain sensitivity level so the body needs to produce enough of the antibodies before the test can detect them. Many people have a detectable level of antibodies within a month of infection, most by three, and nearly 100% by six.
The test that directly tests for the virus is indeed more difficult and expensive, as well as taking much more time (a few weeks, iirc; antibody tests have been developed that can tell you if you're positive within 30 minutes). It is, to my understanding, usually only used if the first test is positive.
Just bit of information on the subject from memory.
I am woefully behind.However, it is true that the basic screening test is for the antibody to the virus, rather than the virus itself. The test tends to be very sensitive, but not as specific; in other words, there are a lot of false positives, but few false negatives. It's the combination you want in a screening test.
If the first antibody test was positive, a secondary test was performed, for the antibody again, which is VERY specific. This will weed out false negatives and confirm positives.
The reason I deferred to Wampus on the testing stuff is that I haven't kept up with the antigen testing... testing for the virus itself. It sounded like perhaps she had done some research, so I'm willing to go with that. If the antigen test is in place, her statement "testing every donation is the only way to ensure safety. Apparently that's already done for HIV, so gay men certainly should be allowed to donate" is totally true.
But back in the day, testing was NOT perfect, because testing for the antigen itself was not commonly done. Hence the screening for high risk behaviors. Testing was not good enough to do the best job possible protecting blood product recipients from the virus, without "banning whole sectors of the population from donating". That may well be an important part of keeping our blood supply safe. Those populations should be screened on high risk behavior, strictly. This shouldn't be a social statement, but a fact-based medical decision.
There was (and apparently is!) an antigen test available, but it was not commonly used for screening for HIV, due to costs, I believe... and time! A test that takes weeks before the blood can be used for donations is useless... red blood cells only "live" outside the body for something like 21 days. After that, the blood's pretty useless. Accurate, timely testing is the goal.
The scary part of not having an antigen test as part of the battery of tests performed is that people tend to be the most "antigenic", or full of virus, directly after they are infected. This is a period before the commonly tested-for antibodies can be made to a detectable level (by a person with a competent immune system). So these folks are not going to be "caught" by any screening test for antibodies... they don't have them, yet... they are walking HIV virus factories, but they feel, act, and look fine. Scary stuff.
(The other time people tend to be very antigenic with negative antibody levels is at the endpoint of their disease... HIV attacks the immune system, after all. These people would NOT otherwise be healthy, though.)
Anyway, I will check tomorrow, if I have time. I walk by that blood bank every day!
Oops. I meant to... I even thought about it several times... and then I didn't. I will eventually... I promise.
My screening test came up positive for HIV twice for our local community blood center. My blood had to be taken to the next level, which was the Western-Blot (which tests more specifically for antibodies to HIV). The second time that was done, however, it was also inconclusive, and they had to do the DAT (direct antigen test) for HIV. That was negative, as it should have been since I have no risk factors other than being a lab tech (but not sticks or anything).
Apologies for repeating myself if I did!)
We're still reeling over here. She was only 53!! 
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