There is no harm in taking an STD test straight after a potential exposure. However, you need to be aware that a false-negative result may occur if a sample is collected in the window period post-exposure. This window period refers to the time between exposure and when a laboratory test can detect the infectious agent. Note that the window period differs from the incubation period (time from exposure to development of symptoms).
Window periods vary for different STDs and also for the laboratory test that is being used:
Metaphase screens for chlamydia, gonorrhea, and trichomoniasis using nucleic acid amplification tests. The window period for these STDs is predicted to be around 5 days, but may be up to two weeks.
Our hepatitis B test detects the hepatitis B surface antigen (HBsAg) and antibodies to the hepatitis B core (anti-HBc), which can take 30 to 60 days to become detectable.
Antibodies to hepatitis C may be detected with our test as early as two weeks post-exposure, but are generally not detected until 8-11 weeks post-exposure, and can be longer in individuals that lack an adequate immune response.
Metaphase uses a 4th generation test for HIV that can detect an HIV infection within 18 - 45 days, or sometimes as early as two weeks post-exposure. Individuals who have been potentially exposed to HIV should be tested immediately, and then tested again at six weeks, three months, and six months. In addition, if an individual is concerned about being exposed to HIV in the last 72 hours, they should be referred to a health care provider immediately for post-exposure prophylaxis (PEP) evaluation.
Syphilis can usually be detected with our laboratory assays around one month post-exposure, but may be up to three months.