How accurate are the 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

  • complete additional tests in a clinic after a ‘reactive’ result.

A ‘window period’ means the time it takes for an infection to show up in tests. This period 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 are used by many NHS clinics.

If you have any STI symptoms, you should visit your local sexual health clinic.

How accurate are chlamydia and gonorrhoea tests?

The chlamydia test and gonorrhoea test are 99.9% accurate. But no test is 100% accurate. If you have any questions about your test results or your risk of infection, contact us.

Your chlamydia or gonorrhoea test will be more accurate if you wait at least 2 weeks after having unprotected sex before testing. Your test kit could include:

  • a vaginal, rectal or throat swab

  • a urine sample pot.

How accurate is the syphilis test?

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

Blood tests for syphilis are most accurate 12 weeks (3 months) after infection but may show a positive result sooner. If you think you might have been exposed to syphilis, you should test now and do another test after 12 weeks.

Our lab needs 16 drops of blood to run an accurate test. You will need to fill the blood sample tube up to the ‘600’ line.

Check our top tips for taking a blood sample.

If you have tested positive for syphilis in the past, it’s likely that you will always get a positive result from a blood test, even if you’ve had treatment. In this case, we recommend that you visit a clinic for an RPR test. This will tell you if you have a new syphilis infection.

How accurate is the HIV test?

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

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

  • Insti HIV test - results are most accurate 3-12 weeks 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.

How accurate is a negative result for the HIV test?

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

Our HIV tests are very sensitive. A negative result is highly accurate as long as you waited for the correct window period after potential exposure to the infection. So if you have a negative result after the window period then you can be confident that you don’t have HIV.

How accurate is a reactive result for the HIV test?

A reactive result means that the test has reacted with something in your blood that could be (but is not necessarily) the HIV virus or antibodies to the HIV virus.

We follow the World Health Organisation guidance on HIV testing. This means that we only diagnose HIV after completing 3 separate tests. These tests look for 3 different parts of the HIV virus or its antibodies.

If your blood is taken in a clinic, there will be enough blood to do all the tests on one sample. With a home sample kit and the insti test, you will only collect a very small sample of blood. This means that the laboratory only has enough blood to do the first of the 3 tests.

The test that we use is very sensitive, to ensure there are no false negatives results. It's so sensitive that there are some things other than HIV, for example other infections, that may cause a reactive result.

If you have a reactive result, we'll ask you to go to a sexual health clinic where they can collect a larger sample to complete the second and third tests. Between 6% and 35% of reactive results will be confirmed as positive in a clinic.

If you are worried about a reactive result or are anxious about waiting for another test, contact our clinicians. We can talk you through the process and answer your questions.

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.

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

The test we use is about 98% accurate in detecting antibodies for hepatitis B or C. If your test is positive, we will refer you to a liver specialist. They will find out whether you have an active infection or not and organise treatment if required.

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

If you are a man who has sex with men then we recommend the hepatitis B vaccine. You can arrange this at your local sexual health clinic.

Written by Dr Paula Baraitser. Medical Director

Last updated at: 08 March 2022