Thank you for the inquiry. From what we gather from the question you were asking about the window period for HIV infection, and accuracy of a fourth generation test. The window period is the time between after HIV infection and before seroconversion (1). Seroconversion is the phase of an infection when antibodies against an infecting agent are first detectable in the blood. During an infection, antigens enter the blood and the immune system makes antibodies in response (2).
After 12 weeks of acute infection, you should have antibodies specific to HIV. It is possible for a person to not produce antibodies to HIV but that is in very rare and specific cases of immunodeficient individuals who are unable to make any antibodies. If you were not making any antibodies, the virus would be continuously replicating unchecked and therefore could be detected through an RNA test, or through a test for the p24 antigen. The p24 antigen is a protein associated with the viral capsid or core (3).
A fourth generation test is a combination test that checks for the presence of antibodies AND the p24 protein antigens. p24 antigen is from HIV, and if no antibodies were being made you would be able to detect it because there would be no antibody-antigen complex (3). Notice in the figure below, as the level of antibody increases in the blood, the p24 antigen decreases. A fourth generation test has essentially a zero percent chance of giving a false negative result after 50 days (4).
Recommendation: Refer to a healthcare professional for other health related questions.
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1.) Window Period
2.) Immunology Basics
3.) p24 Antigen
4.) Probability of a False Negative Result During Window Period.
Figure used (4).