Good afternoon Doctor. I don't know if my question is confusing or not. I had what everybody would consider a "low risk" exposure. Oral sex was performed on me by an HIV unknown. I went to my doctor 4 weeks after the incident and he told me the chances were very low just about zero that I could have contracted HIV in this manner. Anyway I asked him If I should get a PCR/RNA test. He said that an Elisa test was warranted after 4 weeks because it is much more sensitive than the other and is a better test to take. The test came back negative after 4 weeks. Has it ever been seen that a 4 week test came back negative and then came back positive after lets say 12 weeks. or if seroconversion was occuring when blood was drawn would the test come back lets say indeterminate? I hope this is not too confusing. Do you even recommend a 12 week Elisa for this exposure?

An antibody test at 4 weeks is not sufficient to rule out HIV infection. And yes it can turn positive after 4 weeks.