Can you have an STI even if you tested negative?

Reviewed by our clinical team

If you’re sexually active, there’s always a bit of risk associated with having sex with a new or casual partner. This is the case even if you use condoms – although it’s true that condoms do reduce your risk of STIs significantly.

Many STIs – including the most common one, chlamydia – don’t always cause symptoms in their early stages. This means that you might not know you’re infected until you get tested.

However, STI testing is complicated by the fact that different infections have different “window periods”. Certain STIs will show up on a test within a couple of weeks of infection, while others will take much longer. This means if you test too early for certain STIs, the infection might not show up. 

In other words, it’s possible to have an STI even if you tested negative the first time.

How soon after unprotected sex can I test for an STI?

Different STIs have different incubation periods, and therefore different testing windows. Below you’ll find the testing window periods for some of the most common STIs in the UK.

14 days after exposure 

• Chlamydia 
• Gonorrhoea

45 to 90 days after exposure 

• HIV – certain types (including Online Doctor’s HIV tests) can detect the virus sooner than others 

12 weeks after exposure 

• Syphilis

Two of the more common STIs in the UK – genital warts and genital herpes – can only be diagnosed if you’re having symptoms. If you develop any lumps, growths, sores or blisters around your genitals, you should go to the sexual health clinic to have a physical examination. 

What happens if I get a test too early?

If you get a test too early, it may not pick up the infection, which means you run the risk of getting a misleading result. To avoid this, you shouldn’t use an STI test without speaking to a doctor or nurse first, as they’ll be able to advise you on the best time to get tested.

There are some circumstances where you might be advised to take more than one test. If you think you’ve been exposed to HIV, for instance, you might be told to get a test as soon as possible, followed by another test to confirm the first result a few weeks or months later.

Should I wait to get tested if I’m having symptoms?

No, if you’re having symptoms you should go to a sexual health or GUM clinic. A doctor or nurse can give you a test, assess your symptoms and – if necessary – give you a physical examination. If they think there’s a strong chance you have an STI like chlamydia, they might prescribe treatment before you get your test results back. 

Is it safe to use home STI test kits?

Yes, it’s safe to use home STI tests, as long as they come from a trusted provider e.g. the NHS or a registered high street pharmacy like LloydsPharmacy.

At Online Doctor we use a secure form to ask you questions about your sexual history, the last time you had sex, and whether you’re having any symptoms. If clinicians don't think it would be a good idea for you to use a home test kit, they’ll let you know and advise you about what to do instead. 

Can STI test results be wrong? 

These days, STI tests are very reliable, which means you’re unlikely to get a false result provided you’ve tested for the correct STIs at the correct times.

One notable exception would be a test that doesn’t collect a sample from the correct area of the body. Although most STIs affect the genitals, some – including gonorrhoea – can affect the rectum, the throat, and even the eyes. If you take a gonorrhoea test that only involves a sample from your genitals, it may miss the infection elsewhere in your body. 

What should I do if I think I’ve been exposed to HIV?

Becoming infected with HIV is life-changing, but with early diagnosis and treatment you can live a relatively normal and healthy life. For this reason, if you think you’ve been exposed to HIV, you should seek medical advice as soon as possible.

You may even be able to avoid infection altogether if you seek emergency treatment after unprotected sex. Post-exposure prophylaxis (PEP) is a medication that can be taken in the weeks following unprotected sex to prevent infection with HIV.

References

https://www.letstalkaboutit.nhs.uk/worried-about-stis/testing-treatment-of-stis/
https://www.nhs.uk/conditions/genital-warts/
https://www.nhs.uk/conditions/genital-herpes/
https://www.nhs.uk/conditions/hiv-and-aids/diagnosis/
https://www.nhs.uk/conditions/chlamydia/treatment/
https://www.nhs.uk/conditions/gonorrhoea/diagnosis/