Q. My fourth generation antigen-antibody test is negative. Is it necessary to do a retest?

Answered by
Dr. Sadaf Mustafa
and medically reviewed by iCliniq medical review team.
This is a premium question & answer published on Dec 05, 2019

Hello doctor,

I had two sexual encounters with women whom I do not know their HIV status. Both were vaginal and a condom was worn. In the fourth and fifth weeks, I had a fourth-generation antibody-antigen test performed and it came back negative. Should I be retested again?

Dr. Sadaf Mustafa

General Medicine Internal Medicine


Welcome to icliniq.com.

It is a good idea to get repeat testing, here is why. The antibody testing at the fourth and fifth weeks can give you some idea of the HIV (human immuno deficiency virus) status, but the one at 12 weeks after the exposure will confirm the negative status completely. The reason being the window period.

The window period is a duration where a person can have HIV but still test HIV negative. The fourth generation is antigen-antibody based testing and the best we have so far for screening. When suspected acute HIV infection or high risk exposure, PCR (polymerase chain reaction) is the best in the fourth and fifth weeks post-exposure.

Of note, the window period for a fourth-generation antigen-antibody test is short as compared to other HIV tests available (about four weeks). Usually by this time, 95% of infection will be detected in the blood. In general, there is a three month window period for HIV after a given exposure, and therefore for the fouth generation testing to confirm that a person is more than 99.9% infectious. Hence the 12 weeks retesting is recommended.

I hope this helps.

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