Regarding combination HIV antigen/antibody tests, results are more than 99% conclusive four weeks (28 days) following an exposure. Results of these tests become entirely conclusive at six weeks (42 days) following exposure to an infected sex partner. 

 As long as you have not taken anti-HIV medications during this time, the test results you mentioned above effectively rule out the possibility of an HIV infection. I see no reason for further testing. I hope that this information is helpful to you. Take care. EWH

Thank you for your kind reply. It has given me reassurance. The potential exposure was with a partner I was in a six-week exclusive relationship with, after which she did an HIV 1 antibody and antigen test that came out negative. Why don't they test for HIV 2 in the U.S? I had calculated my window period after the day we broke up and ceased unprotected sexual contact. Therefore, if she was negative after a six week window period (which was the total duration of our relationship), there wasn't even a necessity for me to do testing in the first place? Also, can you please explain why some health organizations recommend testing after 3 and even up to 6 months post-exposure? Does the fact that I did both the antibody/antigen test together with PCR rule out possible infection?  And what are some disadvantages of the PCR HIV test, besides the higher costs and rare false negatives?

Dear Dr. Hook, 

Thanks again for your expert advice. What is the theoretical risk of testing positive 90 days (after a negative PCR and antibody/antigen test after 31 days of potential exposure)? Based on your experience, have you ever had someone turn positive after three months? 

kind regards,