Welcome to our Forum. The risk of infection in the situation you mention is very, very low and not something to worry about.
There are no "best" tests for detection of HIV. The test that has been recommended to you is a PCR test in which HIV RNA is used to amplify HIV DNA. It is a very good test although it has somewhat more false positive tests than other antibody tests. for this reason, on this site we do not recommend PCR tests for HIV diagnosis. I have pasted a recent comment I made about PCR tests in below.
"In general we do not recommend HIV PCR testing for diagnosis is HIV infection for several reasons. While the PCR is likely to become positive more quickly than other antibody detection tests (i.e. usual blood tests), at the present time the blood tests are becoming more and more sensitive and detecting infection earlier and earlier so that the time difference in detection between PCR test and antibody detection tests is becoming smaller and smaller and at present is, in general only a week or two. In addition the time course over which the PCR tests become positive is less well described than for the blood tests and, as a result, it is difficult to make a definitive statement on what a negative PCR test means at any time within a few weeks of exposure to a HIV infected or possibly infected partner. PCR tests are also more expensive than regular antibody tests. Finally and most importantly, the false positive rate for PCR tests (i.e. a positive result in persons who do not have HIV) is higher than for blood tests. Each of this on this Forum have seen a number of people who were worried needlessly because of false positive tests. For all of these reasons, we rarely recommend testing for HIV diagnosis using PCR."
At present the type of HIV diagnostic tests which provides an accurate diagnosis most quickly are the so-called "DUO" tests which detect both HIV P24 antigen and HIV antibody. At negative result using this test at 4 weeks following exposure should be considered definitive evidence that infection did not occur and has a lower probability of a falsely positive result than the PCR tests.
Thank you so much Dr. Hook. That was what I was worried about too - the false positive with the PCR. I will try and get the DUO test done instead. However, day 28 happens on a Saturday when the lab is closed, is it better to do it on Friday (day 27) or Monday/Tuesday (day 30/31)?
Dr. Hook, I am in the US now, is this test available here? I could not see that either Quest or Labcorp has this test. Thanks!
Yes, the combined p24 antigen/HIV antibody test is available and approved by the FDA. It is made by Abbott. Some people refer to it as a 4th generation test. I would suggesst you call a local HIV testing group such as an AIDS organization or your health department and ask about its availability