Expert: Terry B - 1/20/2008

Question
QUESTION: I have heard of a certain type of antigen test... p24 is it?  Well, I have read somewhere that the window period for a certain antigen test is about 16 days after exposure.  Is the p24 test the one?  Is there another one? If a test were taken on day 16 itself then, would it be considered conclusive?

ANSWER: Dear Xyz:

Peace and all good things.  p-24 antigen testing is just one of an array of tests to identify possibility of HIV infection.  By far, the most widely recommended is the ELISA/Western Blot test, which searches for antibodies and is about as conclusive as lab testing gets at 6 months.  Some research suggests that the antibody test is reliable as early as six weeks from exposure in most people.

The difficulty with p-24 and several of the tests that are used closer to exposure is often the possibility of "false positives" - this is because these tests are designed to look for anything that 'looks like' HIV - and for some tests, up to 10% of results are something that 'looks like' HIV but is not - causing undue anxiety.  

I hope this provides the information you need - a test at day 16 would not be considered conclusive - but might be a good indicator if it is negative (non-reactive).  What is important with such a test is that a positive (non-reactive) result does not necessarily mean HIV infection.

More detailed information about p-24 antigen testing, as well as other options, can be found at:
http://www.avert.org/hivtesting.htm#q7

I hope this helps.

Best to you and yours,

Terry



---------- FOLLOW-UP ----------

QUESTION: Well, I tested negative... WOOHOO!  You said that a "non-reactive" result is a good indicator that I don't have HIV.  Did I understand you correctly?

Answer
Dear Xyz:

Wahoo and good for you!  Yep, non-reactive is lab slang for not positive.  Learn from the experience!  And read on at www.thebody.com or www.avert.org for ways to protect and enjoy yourself and your loved ones in the future!

Best to you and yours,

Terry