Yes, you should feel pretty good about negative results from a 4th generation, antigen/antibody combo test with a blood sample taken 33 days after your last suspected exposure. By day 21, an ELISA test like the one you describe would react positive for most infections. By day 48, it would catch almost all infections. By day 90, you could consider negative results to be officially conclusive. What most clinicians would advise right now is that you breathe a sigh of relief and take a second test at or after the 90-day mark to confirm your results. Two tests are considered to be standard and prudent. No HIV test is reliable for negative results at only 14 days post-exposure. The 4th-generation test you refer to would be a combination antigen/antibody assay. Such tests could certainly detect an HIV infection at 14 days, but that's only the beginning of the so-called window period that needs to elapse before negative results are conclusive. Timing for antigen/antibody tests is generally as follows: Most infections are detected by 21 days after exposure. Almost all infections are detected by 48 days after exposure. Negative results can be taken as conclusive at 90 days after exposure. The NAAT test that you refer to is a PCR test that looks directly for viral RNA. It's sometimes called a viral load test. It may very well be that an infected person would have a detectable viral load 14 days after exposure. Many infected people would be expected to have a very high viral load at that point, as a matter of fact. That isn't always the case, however. Sometimes viral levels remain low for quite a long time, low enough for the PCR test not to detect significant quantities of viral RNA. Public health authorities advise that viral load tests should not be used to rule out HIV infection. Antigen/antibody tests can be used to rule out HIV infection, but according to the timeline outlined above. Combination antigen/antibody tests for HIV are considered to be over 98 percent reliable for negative results at 48 days post exposure. They are considered conclusive for negative results at 90 days. The 90-day standard has quite a lot of confidence buffer built into it. So, by 80 days, you could have virtually complete confidence in negative results. A negative result anytime after about 48 days would be cause for a huge sigh of relief, with prudence dictating a final, follow-up test at 90 days or later to rule out anomaly. Public health authorities recommend a minimum of two tests in any case, just to rule out the minimal possibility of lab error. A 4th-generation, combination antigen/antibody ELISA assay is limited in reliability by the amount of antigens and antibodies present in the blood of an infected person. The subject is complicated, but in general, reliability of negative results increases on a curve as a function of time. There's actually a small, anomalous bump intitially after exposure as high viral loads can result in high antigen count. That drops off quickly, usually. After that point, antibody production increases fairly predictably. At 21 days post exposure, well over half of all infections would be detected. At 48 days, almost all infections would be detected. By 90 days, public health authorities advise that negative results can be considered conclusive. So, at the six week mark, or 42 days, you can have a great deal of confidence in negative results. Breathe a sigh of relief and have a final test at 90 days or after as confirmation. That would be the advice you'd receive from most experienced HIV clinicians.