From: jfurr@polaris.async.vt.edu (J. Furr)
Newsgroups: alt.folklore.urban,talk.politics.medicine
Subject: Re: Why care what percentage?  (was: Gay Likelihood)
Date: 11 Jan 93 18:14:34 GMT
Followup-To: talk.politics.medicine
Organization: Virginia Center for Lemur Fandom, Blacksburg, Virginia, USA (subscribe to alt.fan.lemurs TODAY)

In article <1is73fINN7qt@lynx.unm.edu> bhjelle@carina.unm.edu writes:
>In article <wLT3wB3w165w@codewks.nacjack.gen.nz> system@codewks.nacjack.gen.nz (Wayne McDougall) writes:
>>geb@cs.pitt.edu (Gordon Banks) writes:
>>
>>Does testing of the blood supply involve testing for the virus itself or for 
>>antibodies to the virus? The reason I ask is that blood testing was introduced
>>before there was a test for the virus itself. I understand that testing
>>directly for the virus is still not cheap and I imagine that on the scale
>>required for testing the blood supply, it could be quite expensive.
>
>The overwhelming majority of HIV testing that goes on in blood banks
>and elsewhere is antibody testing. Cost is not the only reason for
>that - it is a fact of life that antibody tests, for most viruses,
>are infinitely more reliable than tests for antigen or viral
>nucleic acid (such as PCR). We are still a long way away from
>routine PCR testing of blood donations -trust me, I have done
>hundreds of PCR assays myself.
>
>Only antibody tests are licensed for detection of HIV, HTLV,
>HCV, and no one can substitute another test.
>
>>My concern is that if someone has the virus before developing antibodies, 
>>then that won't be detected if only the presence of antibodies is tested.
>>
>>I've asked lots of doctors, etc, and no one can give me a straight answer.
>>
>This is a major concern of all blood bankers. A large number of studies
>have been done to try to assess the current risk of HIV in the blood
>supply, and generally converge around 1 in 60,000 donations as
>HIV-contaminated. A sizable fraction of false-negative tests for
>HIV antibodies are due to donations made during the "window period"
>between exposure and development of antibody in the donor (as
>opposed to prolonged seronegativity, human error in testing, etc).
>
>The good news is that, in the period since most of those studies
>were done, blood bank screening tests have greatly improved in
>their ability to catch early HIV infection, due primarily to
>greater sensitivity to the (early) IgM antibody response.
>
>>ObUl or fact? To save the costs of test, blood is tested in binary chops.
>>Eg 100 samples are tested. If there is no response, its all accepted. If there
>>is an positive reading, then two tests are performed breaking the samples into
>>50 and 50, and so on. (Hmmm, would be better to start with 128 samples....).
>
>Some schemes like this are being used in the 3rd world, not in the US.
>
>>country for antibody tests. Is it common or widespread? I would imagine that
>>it would be a productive technique in western countries where we would still
>>expect no result from testing 100 people. (At this rural hospital, over 50%
>>tested positive for AIDS - community based testing showed 35% positive).
>
>This would never pass muster with FDA. Count it out.
>
>>Wayne "O Rh- Kell- Duffey-  THE UNIVERSAL DONOR" McDougall
>
>Keep on donating!
>
>Brian

Please move this thread OUT of alt.folklore.urban.  talk.politics.medicine
can deal with as they please thereafter.
Newsgroups: alt.folklore.urban