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Failures in fourth generation tests
Oct 8, 2013

Hi! I've read in some reliable websites that there is a problem with the Ag/Ab test. They say that the test detects the antigen (p24), but after 28 days, the p24 starts to disappear and the test will detect only antibodies. So, if you haven't produced antibodies yet, and the p24 has already disappeared, the result will be a false negative. Is it true? I (as a high school student) don't think it's true because the p24 is in the virus, and for the virus to be indectable in the Ag test, you must have produced antibodies, as they "kill" the virus, then the test will really tell you if you have HIV. Anyway, I got test eight weeks after my exposure (whose risk was very very low), with an Ag/Ab test. Do I have to get tested again?

Response from Mr. Cordova

Hi there,

Thanks for writing in.

By 28 days most people will have produced enough antibodies that can be detected by an antibody test. There is enough overlap between when the body starts to produce enough antibodies and when the level of the p24 antigen fall off that that a combo antibody/antigen test is able to reliably pick up an infection early on. A 90 day antibody test is still required to determine a true negative result.

I agree with you, p24 antigen levels start to fall as the body begins to produce antibodies. These antibodies would be produced in sufficient enough quantities that could be detected by the test. If not, it is likely that the levels of the p24 antigen would still be high enough that could be detected by the antigen portion of the test.

Your eight week test is a great indicator of your true status. If you want a conclusive result I would suggest a test at 90 days.

I hope this helps.

In health,

Richard



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