STI window period: when to get tested after a risky sexual encounter
The window period is the time between a risky encounter and the moment a test can detect the infection. If you test too early, the result may be negative even if you are infected. So the question is not only which test to take, but when.
First: if the risk was less than 72 hours ago
If you had an HIV risk (for example, sex without a condom with a person living with HIV or of unknown status) less than 72 hours ago, go to an emergency department: there is preventive treatment (post-exposure prophylaxis, PEP) that works best the sooner it is started. Testing comes afterwards.
Approximate window period by infection
Chlamydia, gonorrhoea, trichomonas, Mycoplasma and Ureaplasma (PCR on urine or genital sample): from 1–2 weeks.
HIV (blood test): most infections are detected at 4–6 weeks; a negative result at 6 weeks is usually considered conclusive.
Syphilis: usually from 3–6 weeks; in some cases repeating at 12 weeks is recommended.
Hepatitis B: from 3–6 weeks.
Hepatitis C: antibodies usually appear between 8 and 12 weeks.
Herpes: the most reliable option is to test a lesion (sore or blister) when it appears.
These timeframes are approximate and can vary by person and type of test. In the included medical consultation we tell you the right moment for your case.
The most practical strategy: two moments
At 2 weeks: test for bacterial infections (chlamydia, gonorrhoea, Mycoplasma, trichomonas). If something is found, it can be treated early.
At 6 weeks or later: blood test for HIV, syphilis and hepatitis to confirm.
If you have symptoms (burning when urinating, unusual discharge, sores, itching), don't wait until the end of the window period: get tested now.
Frequently asked questions
Can I get tested the day after the encounter?
You can, but it won't detect such a recent infection. It only shows whether you already had an earlier infection. To rule out the recent contact, you need to wait for the window period.
If the test is negative too early, am I in the clear?
Not entirely: it's best to repeat the test once the window period for each infection has passed.
What technique do you use?
At Sermed Laboratorio we use Real-Time PCR, a highly sensitive technique, with same-day results if the sample is taken before 4:00 pm.
Get tested in Barcelona without an appointment – Carrer del Dos de Maig, 283 (Eixample). Medical consultation included.
For guidance only: this does not replace a medical consultation or diagnosis. If you have severe symptoms or an emergency, call 112.
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