I really really doubt that ketamine would interfere with that, ketamine is a substance that does not bear resemblance to biological molecules afaik so even if the HIV test would depend on detection of simple chemical molecules I don't think a false positive or false negative would happen like that. But I think a HIV test actually looks for antibodies to the virus so that has zero to do with it. Ketamine looks nothing like such an antibody, its not even remotely on the same scale (chemical vs biological) so no doctor is mad enough to confuse them.
Low-dose ketamine affects immune responses in humans during the early postoperative period.
That means that if you have
just had a medical operation performed on you and take even small doses of ketamine it compromises your immune system.
But I also think that if you aren't in the hospital whatsoever that frequent ketamine use weakens your immune system. In the full-on AIDS stage it's definitely something to stay away from but there are more drugs that weaken your immune system, so theyre all pretty much not-done then.
This thread will be closed as it is answered and you posted anonymously, in the case you have questions about this like reopening the thread with additional purpose or questions for me personally I advise you to private message me.
all the best, my friend..

But in short, the mention of immune system is coincedental so I do not think you have to worry.
If you have a pretty good reason to have this HIV test, like more than casually or after a couple times unsafe sex maybe you shouldn't ask here or listen to me but call the people that do the test and ask them. If you fear that they will discover your drug use have a buddy of yours call, or call anonymously.