STD test after unprotected sex in London: when to test, what to do first

The most common question we hear after an unprotected sex encounter is: how soon can I get tested? The honest answer is that testing too early is just as problematic as not testing at all. Every STI has a window period, and testing before that window closes can produce a false negative result that gives false reassurance.

This guide tells you exactly when to test for each infection, what to do in the first 72 hours if the exposure was high-risk for HIV, and how private testing at MDC Baker Street works once the right time has come.

The window period is the time between exposure and when a test can reliably detect the infection. Testing within the window period may produce a negative result even if you are infected. This is not a failure of the test. The markers it looks for simply are not present in detectable levels yet.

A practical approach for most people: book a first test at 7 to 14 days to cover chlamydia, gonorrhoea, trichomonas, and mycoplasma. Then return at 28 days for the full panel including HIV, syphilis, and hepatitis. This two-stage approach is the most clinically thorough way to confirm your status after a single unprotected encounter.

If your exposure was low-risk and you want a single visit, attending at 28 to 45 days post-exposure gives you the most comprehensive single result covering all infections in the panel.

The first 72 hours after a high-risk exposure are the only period where an intervention can prevent infection rather than just detect it. There are two interventions relevant in this window.

The most important thing to understand about STI symptoms is that most infections produce none at all, particularly in the early stages. Waiting for symptoms before testing is not a reliable strategy. That said, some infections do produce symptoms that appear within days to weeks of exposure.

If you have no symptoms, this does not mean you are clear. Most people with chlamydia, gonorrhoea, and HIV have no symptoms at all during the early weeks after infection. Testing at the appropriate window period is the only way to know your status with certainty.

The right panel depends on the timing of your visit relative to the exposure and the nature of the exposure.

For chlamydia and gonorrhoea, a negative result at 10 to 14 days is reliable. For HIV and syphilis, a negative result at 10 days means very little clinically. You are still within the window period for both and need to retest at 28 days for a result that means anything. Do not assume a negative at 10 days clears you for all infections.

Yes. A condom failure carries a similar exposure risk to unprotected sex for most STIs. The same window periods and testing approach apply. Testing is recommended at the same intervals as for unprotected sex.

The risk from oral sex is lower than from vaginal or anal sex but is not zero. Gonorrhoea, chlamydia, syphilis, and herpes can all be transmitted through oral sex. If you are concerned, a test at 7 to 14 days for chlamydia and gonorrhoea and at 28 days for syphilis is appropriate. Mention the type of exposure when you attend so the clinician can advise on which sample sites to use.

No. Testing at MDC is entirely private. Your result is never shared with your GP, the NHS, or any third party. Nothing appears on your medical record. See our confidential STD testing page for more detail on how privacy works at MDC.

A clinician will contact you directly to explain your result and advise on next steps. For most bacterial infections, treatment is straightforward and highly effective. For HIV, our clinical team will guide you to the appropriate NHS specialist service, where antiretroviral treatment is available free. A positive result is the beginning of a managed process, not a crisis without a path forward.