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How quickly can HIV antigens be detected after infection

Dec 11, 1996

If a person contracted the HIV virus and ten days later was tested for HIV antigens in the blood, would it be detected? What is the minimum period of time after infection that HIV antigens could be detected?

Response from Mr. Sowadsky

Hi. Thank you for your question.

The p-24 antigen test will pick up an infection an average of 6 days prior to a person testing antibody positive. The p-24 antigen tests will often show positive 2-3 weeks after initial infection. However, not all recently infected persons have detectable levels of p-24 antigen in their blood. So a negative p-24 antigen test does not necessarily mean the person is not infected. Once the person turns antibody positive, the p-24 antigen test will often revert back to a negative result. So this test will only be positive for a short period of time.

The antibody tests show positive an average of 25 days after infection. The usual period of time that most (but not all) people will show positive on the antibody test is 3 months. The maximal amount of time that a person starts to show antibody positive (in more than 99% of cases) is 6 months.

So we can say that the antigen tests will pick up an infection about 6 days before the antibody tests will turn positive. Getting an antigen test at 10 days would usually not pick up the infection. Let me also stress that the p-24 antigen test alone CANNOT be used to diagnose HIV infection. Remember, this test will not always pick up an infection. A p-24 antigen test (whether positive or negative) must always be used alongside other HIV diagnostic tests, before a persons HIV status can be determined.

If you have any further questions please e-mail me at "" or call me at 1-800-842-AIDS.

Immunizations, Viruses, & Inconclusive Test Results

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