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there are so many uncertainties!

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it is said that the standard antibody tests are over 99% accuate. now i have a question about that.
are they 99% accurate at a specified amount of time after possible exposure? does this mean that someone with a negative result from an antibody test at 6 months should be over 99% sure they are in fact negative? people have so many questions about this. it seems like there are so many uncertainties regarding hiv testing. what happened in science that leaves people so uncertain after numerous negative hiv tests? its funny that if you get tested for something that is not life threatening and the result is negative you'll never think about it again.


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replied April 7th, 2011
HIV and AIDS Answer A21648
Hello and thank you for your post on e health forum.

From the question, it seems that you want to know if the test results change with the duration of the sickness, and the chances of having a wrong result at any point of time.

Please understand that tests for HIV (ELISA) detect the presence of antibodies to HIV, which usually present within 4 - 12 weeks of exposure, depending on the severity of exposure (Probable no of virions that might have entered the blood stream).

Hence once antibodies are synthesized by the body, they remain in considerable amounts as long as viremia is present.

Hence the chances of very sensitive tests (like ELISA) giving a negative result, in presence of antibodies to HIV, is very negligible.

if antibodies are present - the test is positive, if they are absent - the test is negative. It is as simple as that.

There is no reason to doubt test results if they are done at the correct interval.

The best time to do a ELISA test for HIV antibodies is after 4 weeks of exposure. 90% of normal individuals who have HIV exposure, will seroconvert within 4-6 weeks. The sensitivity of the ELISA test is 99.9%.

If a test once done after 12 weeks of exposure - is NEGATIVE, the chances of developing antibodies to HIV at a later date will be negligible. Hence there is no need to repeat the test again.

But usually clinicians tend to be cautious and ask patients to repeat the test again and again, causing severe stress and anxiety. But this is not necessary.

I hope this helps.



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