How long it takes to test positive for a disease such as an STD depends on a number of factors. These include:
- Whether the test is looking for the pathogen that causes the disease, or your immune response to the pathogen.
- The specific test that is being done. For example, a DNA amplification test that looks directly for the organizm would usually be able to detect a an infection more quickly than an antibody based test that needs to wait for an immune response.
- The health of your immune system and whether you have been exposed to a similar infection before.
As such, if you are concerned that you might have been exposed to a particular STD, it is important to discuss when that exposure happened with your physician. She will be able to give you a general idea of whether or not you have passed the window period for STD testing or if it would be better to wait and get tested (or re-tested) at a later date.
Testing while you are still inside the window period could lead to inconsistent test results or a misleadingly false negative test. This is why STD screening may not provide an accurate reflection of your health status when you have had unprotected sex relatively recently.
During acute HIV, the virus is replicating but the body has yet to form antibodies. In this case, a clinician can specifically test for the virus itself to assess for acute HIV. There are also specific tests that are suitable for detecting recent HIV infections (less than 170 days old), but these tests are not widely used outside of research settings.