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Accuracy of tests
      #32872 - 04/24/02 09:01 PM

I've heard the accuracy percentages of HIV tests, but I was wondering about something that seems rather logical. Wouldn't an inaccurate HIV test more likely be false-positive, rather than false-negative. Aren't there certain things that cause the test to be reactive? But short of human/lab errors, wouldn't a negative result be even more accurate than what the stated "accuracy percentage" is? Am I wrong in thinking this?

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Re: Accuracy of tests new
      #32887 - 04/25/02 12:23 AM

Yes, you're right, elisa tests are very sensitive but not 100 percent specific, that means they can yeld false positives (i.e. after a flu shot). That's why they're confirmed with a more specific test like the western blot.


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Re: Accuracy of tests new
      #32895 - 04/25/02 01:45 AM

We can go like this for ever.

Elisa can show false positives in approximately 2 to 100,000. Well what that will make in perxentage for being specific. Western Blot is very specific - but not senisitive enough. PCR is more sensitive than Elisa, but only 95% specific.

When specific is mentioned for people that don't understand it means that it can produce false result - usualy false positive rather than false negative.

Outside window period (whether that is 3 or 6 months - meaning which ever is 100% correct) Elisa will always be 100% sensitive and 100% specific (and 1 in 50,000 will get false positive).

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Re: Accuracy of tests new
      #32989 - 04/25/02 11:12 PM

There are over 20 things that can create a "false positive". The strange thing is that most people assume that their positive result is not false positive and so never get re-tested. Those who have re-tested have found that their tests after hav ecome back negative and then they suspect the test is invalid.

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