How accurate are STI tests?

Our simple home STI test kits are highly accurate and reliable when you:

  • follow the instructions carefully

  • wait for the recommended window period before you test

  • do more tests in a clinic after a reactive result for HIV.

A window period is the time it takes for an infection to show up in tests. This starts from the time of your sexual health risk - when you think you may have been exposed to infection.

Find out the best time to test

Your samples are sent to our partner laboratory to be processed by specialist technicians. We use the same tests that many NHS clinics use.

If you have any STI symptoms, you should visit your local sexual health clinic. If you have any questions about your test results or your risk of infection, contact us.

How accurate are chlamydia and gonorrhoea tests?

The chlamydia test and gonorrhoea test are 99.9% accurate if you wait at least 2 weeks after having unprotected sex before testing. 

How accurate is the syphilis test?

Our blood sample syphilis test gives a reliable result when done correctly and at the right time.

Blood tests for syphilis are most accurate 12 weeks after infection but may show a positive result sooner. If you think you've been exposed to syphilis, you should test now and do another test after 12 weeks.

Check our top tips for taking a blood sample.

If you've tested positive for syphilis in the past, you’ll probably always get a positive result from a blood test, even if you’ve had treatment. You’ll need to do a rapid plasma reagin (RPR) test. This will tell you if you have a new syphilis infection. If you tell us about a past syphilis diagnosis, we will make sure you get the right kind of test.

How accurate is the HIV test?

Blood tests for HIV are reliable when done at the right time. We offer 2 types of HIV tests which have different window periods.

  • Lab test - results are most accurate at least 7 weeks (45 days) after potential exposure to the infection.

  • Insti HIV test - results are most accurate 12 weeks (84 days) after exposure.

If you’re not sure when you might have been exposed, test now and then take another test after 4 or 12 weeks, depending on the type of test.

Both types of HIV tests will give you either a negative result or a reactive result.

A negative result is highly accurate as long as you waited for the correct window period after your risk of infection. So, if you have a negative result after the window period then you can be confident that you do not have HIV.

A reactive result means that the test has reacted with something in your blood. It could be a sign of HIV infection, but it’s not the same as a positive result. Read more about reactive results.

How accurate are the tests for hepatitis B and hepatitis C?

Our blood sample test is a very reliable means of testing for hepatitis B or hepatitis C infection. It’s about 98% accurate in detecting antibodies for these viruses.

If you think you've been at risk of hepatitis B or C infection during sex, you need to wait 12 weeks before testing for the most accurate result.

If your test is positive, we’ll refer you to a liver specialist. They will find out if you have an active infection and organise any treatment you might need.

If you know that you’ve been infected with hepatitis B or C in the past, we recommend that you visit a sexual health service to take your test.

If you are a man who has sex with men then you should think about getting vaccinated for hepatitis B. You can arrange this at your local sexual health clinic.


Reviewed by Dr Paula Baraitser. Medical Director
Last updated at: 24 August 2022