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p24 antigen and antibody tests during ARS

Nov 26, 1996

What is the likelihood of both p24 antigen and antibody tests showing negative if they are performed at thesame time during symptoms of ARS? I understand that ARS is associated with high levels of virus and therefore the antigen test should show positive during this time?

Response from Mr. Sowadsky

Hi. Thank you for your question.

It's really hard to say if either the antibody and/or the p-24 antigen test would show positive during acute viral syndrome. Either of these tests may or may not show positive during this time. In terms of the timing of acute viral syndrome, and when the tests will show positive, let me make a quick comparison.

Acute Viral Syndrome: Usually occurs within the first month or so after infection. It lasts for a week or two, then goes away by itself. Not all people will exhibit symptoms due to acute viral syndrome (flu-like symptoms).

HIV antibody tests:

The AVERAGE period of time that an infected person will show positive on the test is 25 days. This is an average, so not all people will test positive by this point in time.

The USUAL period of time that an infected person will show positive on the test is 3 months. This means that most (but not all) infected people will show positive on the test by this time.

The MAXIMUM period of time that an infected person will show positive on the test is 6 months. By this point in time, more than 99% of infected persons will show positive on the test. This is as accurate as any test in medicine could ever be.

p-24 antigen test: The p-24 antigen test will often show positive about 6 days (or a week) before the antibody tests turn positive. This test will often revert back to a negative once antibody tests turn positive. So this test will only be positive for a short period of time.

The important thing to keep in mind is that there is a lot of variability as to when a person may show symptoms of acute viral syndrome, and when they would test positive on the antibody tests and the p-24 antigen tests. We can only give general ranges as to the time points of these (as stated above). Therefore in summary, a person may or may not test positive on these tests during acute viral syndrome. If you have any further questions, please feel free to call the Centers for Disease Control at 1.800.232.4636 (Nationwide). Rick Sowadsky MSPH CDS

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