08-06-2008, 05:25 AM
Hey Hep carrier, let's not get into a tizzy. Hep C is NOT the only strain of viral hep in existence.
As it so happens, Hepatitis B sometimes does cross react with HIV on the ELISA test. BTW, the previous ask er gave a FABULOUS explanation of how the tests work. Before we had HIV testing, CDC officials debated using the Hep B test as preliminary test for HIV, despite lower sensitivity to HIV.
The root of cross-reactivity is in the concepts of sensitivity and specificity. These are measures of test accuracy.
A highly sensitive test picks up a lot of positives, including false positives. A highly specific test eliminates a lot of negatives, including a lot of false negatives.
So ideally, you want a test that is highly specific and sensitive, but balanced enough so that you pick up all the true positives and rule out all the true negatives.
The HIV ELISA test is very sensitive, so it picks up a lot of false positives. Because the immobility is expensive and time-consuming to run (though highly accurate), it's used as a back up to the quick and easy ELISA.
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