Correct that the antigen component of the AgAb (4th generation) HIV tests does not detect HIV2 antigen. But the antibody component detects HIV2 antibody by 6 weeks. The exceptions are sufficiently rare -- and HIV2 sufficiently rare in the US -- that the overall result can be considered conclusive any time 6 weeks or more after the last possibel exposure.

There are no medical conditions -- autoimmune problems or anything else -- that are known to alter the reliability of the current AgAb tests. Although in theory some conditions or medical treatments, like advanced cancer, potent immunosuppressive drugs or cancer chemotherapy, could delay antibody development and thus positive results in an infected person. However, this remains pretty much theory only that actually doesn't happen in real life. And in these conditions the antigen component could be even more strongly positive, and for a longer period of time. To my knowledge, there hve been no reports of false negative AgAb tests in patients with such conditions or treatments.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

That completes the two follow-up comments and replies included with each question, and so ends this thread. I hope the discussion has been helpful. Best wishes and stay safe!