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**** Unprotected sex with prostitute. after 135 days antigan & antibody test negative (CMIA =value 0.42) Do I need to test more or Is this conclusive?


Hello and thank you for your inquiry.

We gather that you would like to know if your 4th generation Ag/Ab HIV test performed at 135 after an incidence of unprotected sex is conclusive.

Unprotected vaginal or anal sex is considered to be a High Risk activity for transmission of HIV. Unprotected sex is in fact one of the primary ways in which the virus is transmitted between people.

Tests that detect the p24 antigen generally have shorter window periods than tests that only detect antibodies. This is because most people have detectable levels of p24 antigen by 20 days after infection, which is generally earlier than antibodies can be detected. However, levels of p24 antigen in the blood begin to decrease three to four weeks after infection and are no longer detectable five to six weeks after infection. This is why fourth-generation HIV tests were designed to also detect anti-HIV antibodies, as antibodies generally remain detectable for the entire course of HIV infection. (1)

Fourth-generation HIV tests can detect HIV infection in 50% of people by 18 days after infection; 95% of people by 34 days after infection; and 99% of people by one and a half months after infection. These tests have a sensitivity of 99.9% (1)

Recommendation: HIV testing is recommended for the situation you have presented. At 135 days after your encounter, your were well beyond the window period for a 4th generation test. You can consider your test results to be conclusive for this specific incident. You might consider using a condom during future sexual encounters to reduce your risk of acquiring HIV.

Regards, AIDS Vancouver Helpline Volunteer, Dyson