Which STIs can be checked with a blood test?

A blood test can check for:

• HIV
• Syphilis
• Hepatitis A, Hepatitis B and Hepatitis C
• Herpes antibodies, although these tests have important limits

A blood test only checks for what the lab has been asked to look for. Doctors choose blood tests according to your symptoms, any conditions you have and any medicines you take. In pregnancy, you’ll be offered tests for HIV, Hepatitis B and Syphilis. Read more in “Would a normal blood test show HIV?”

Many common STIs can’t be found with a blood test:

• Chlamydia, Gonorrhoea and Trichomonas are tested with a urine sample or a swab
• Mycoplasma genitalium is tested with a urine sample or a vaginal swab, usually only if you have symptoms or a partner has it
• genital warts are diagnosed by a doctor or nurse looking at them, and there’s no blood test for HPV
• Herpes sores and mpox are tested with a swab from the sore
• bacterial vaginosis and thrush, which aren’t classed as STIs, are checked with a swab

A blood test won’t find Chlamydia or Gonorrhoea. UK guidelines say urine and swab tests are far more accurate, so older blood tests for Chlamydia are no longer considered suitable. Read more in “How to test for Chlamydia: which sample you need and when”

There are three main kinds of HIV test.

4th generation lab tests

A blood sample, usually from your arm, is tested in a laboratory for HIV antibodies and the p24 antigen, which is part of the virus itself. This is the standard HIV test in the UK. Many infections show up well before 45 days, but UK guidelines say a negative result is only reliable from 45 days after a risk.

Rapid tests and self-tests

These use a finger-prick of blood or a mouth swab and give a result in minutes. Most are older antibody tests. A negative result from any rapid test or self-test is only reliable from 90 days, and a reactive result always needs confirming with a lab test.

HIV RNA tests

These look for the genetic material of the virus, so they can find HIV earlier. UK guidelines don’t recommend them for routine diagnosis, and a negative early result still needs a follow-up test at 45 days.

If you test before 45 days, a negative HIV result needs a repeat test. If you think you’ve been exposed to HIV in the last 72 hours, get urgent medical advice about PEP, a medicine that can stop you getting infected.

The standard Syphilis test is a blood test for antibodies. If you have a sore, a swab from it can be tested too.

A Syphilis test in the first 3 months after sex can miss the infection. The first sore usually appears around 3 weeks after infection, and antibody tests can stay negative for up to 2 weeks after that. UK guidelines recommend a repeat test 3 months after any high-risk contact.

Syphilis antibodies usually stay in your blood for life, even after successful treatment. If you’ve had Syphilis before, clinics use a different blood test, called RPR, to check that treatment has worked and to spot a new infection. Read more in “Can you have Syphilis and not know it?”

Hepatitis A, B and C are all diagnosed with blood tests, but each one works differently:

• Hepatitis A can pass on through close contact, including sex. A blood test shows whether you have it now or are immune.
• Hepatitis B passes on through blood and body fluids, including vaginal, anal and oral sex without a condom. The test looks for part of the virus, the surface antigen, which usually shows up 30 to 60 days after infection. A separate test shows whether you’re immune.
• Hepatitis C mainly passes on through blood. The first test looks for antibodies, which can take 12 weeks or more to appear. If it’s positive, a second test shows whether the infection is still active.

Hepatitis tests need more time than many people expect. If a Hepatitis C test is negative, you may be advised to test again in 6 months, as the test isn’t always accurate after a recent infection. Most adults who’ve had the Hepatitis B vaccine don’t need a test to check they’re immune.

A blood test can look for antibodies to Herpes type 1 and type 2, which show you’ve had Herpes at some point. But these tests have real limits:

• they can’t tell you where on your body the infection is, or when you caught it
• antibodies can take time to appear after a new infection
• false positive results are more common in people at low risk
• up to 12% of people with Herpes lose their antibodies over time

UK guidelines don’t recommend routine Herpes tests for people without symptoms. If you have a sore, a swab from it is the best test. Read more in “How accurate are blood tests for Herpes?”

Yes. Many home test kits use a small blood sample from a finger-prick, which you post to a lab. HIV self-tests give a result in minutes, using a finger-prick of blood or a mouth swab.

A reactive self-test result always needs confirming with a lab test. Finger-prick samples can sometimes be too small for the lab to test, so follow the kit’s instructions carefully. Read more in “How to take a blood sample for a home test”

Better2Know offers:

• Full Screen: tests a blood and urine sample for 7 infections, including HIV, Syphilis, Hepatitis B, Chlamydia and Gonorrhoea, from 28 days after sex, with results in 3 days (5 days for the home test).
• HIV 4th Generation: a lab blood test for HIV antibodies and the p24 antigen, from 28 days after a risk, with results in 1 day. You can book it at one of our clinics or order a home test kit.
• Peace of Mind: tests a blood sample for Syphilis and a urine sample for Chlamydia and Gonorrhoea, from 14 days after sex, with results in 2 days. You can book it at a clinic or order a home test kit.

If you test before 45 days, a negative HIV result needs a repeat test. A Syphilis test in the first 3 months after sex can miss the infection, so you may need a repeat test. Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

How long after sex should I wait for an STI blood test?

It depends on the infection. A lab HIV test is reliable from 45 days, Hepatitis B usually shows up 30 to 60 days after infection, and Syphilis and Hepatitis C tests may need repeating at 3 or 6 months. If you test sooner, you may need a repeat test.

Will a blood test show an STI I’ve had before?

Sometimes. Syphilis antibodies usually stay for life, and Hepatitis A and B tests can show you’re immune after a past infection or vaccination. A Hepatitis C antibody test can stay positive after the infection has gone, so a second test checks whether it’s still active.

Can a blood test find HPV?

No. There’s no blood test for HPV. It’s checked through cervical screening, and genital warts are diagnosed by looking at them.

A blood test can find HIV, Syphilis, Hepatitis and Herpes antibodies, but not Chlamydia, Gonorrhoea or Trichomonas, which need a urine sample or a swab. Whichever test you have, timing matters, so check when each test becomes reliable and repeat it if you need to.

Book a Full Screen at a clinic near you or order a home test kit. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 15 November 2019 and was last updated on 1 October 2026.

This article is general information and not a substitute for personal medical advice.

Sources

1. British HIV Association, British Association for Sexual Health and HIV and British Infection Association, Adult HIV testing guidelines, 2020. https://bhiva.org/wp-content/uploads/2024/10/HIV-testing-guidelines-2020.pdf
2. British Association for Sexual Health and HIV, Summary guidance on testing for sexually transmitted infections, 2023. https://www.bashh.org/_userfiles/pages/files/resources/bashh_summary_guidance_on_stis_testing_2023.pdf
3. British Association for Sexual Health and HIV, UK guidelines for the management of syphilis, 2024. https://bashh.org/_userfiles/pages/files/syphilis_2024.pdf
4. British Association for Sexual Health and HIV, Guidelines on the management of viral hepatitis, 2026. https://www.bashh.org/_userfiles/pages/files/guidelines_on_the_management_of_viral_hepatitis_2026.pdf
5. British Association for Sexual Health and HIV, UK national guideline for the management of anogenital herpes, 2024. https://www.bashh.org/_userfiles/pages/files/pateletal2024britishassociationofsexualhealthandhivuknationalguidelineforthemanagementofanogenital.pdf
6. British Association for Sexual Health and HIV, UK national guideline for the management of infection with Chlamydia trachomatis, 2026. https://www.bashh.org/_userfiles/pages/files/national_guideline_for_the_management_of_infection_chlamydia_trachomatis_2026.pdf
7. NHS, HIV and AIDS, reviewed 9 July 2025. https://www.nhs.uk/conditions/hiv-and-aids/
8. NHS, Blood tests, reviewed 2 November 2023. https://www.nhs.uk/conditions/blood-tests/
9. NHS, Screening for hepatitis B, HIV and syphilis, reviewed 23 January 2024. https://www.nhs.uk/pregnancy/your-pregnancy-care/screening-for-hepatitis-b-hiv-and-syphilis/
10. NHS, Hepatitis A, reviewed 24 April 2026. https://www.nhs.uk/conditions/hepatitis-a/
11. NHS, Hepatitis B, reviewed 17 November 2025. https://www.nhs.uk/conditions/hepatitis-b/
12. NHS, Hepatitis C, reviewed 19 March 2026. https://www.nhs.uk/conditions/hepatitis-c/
13. NHS, Human papillomavirus (HPV), reviewed 10 March 2026. https://www.nhs.uk/conditions/human-papilloma-virus-hpv/
14. UK Health Security Agency, Mpox: diagnostic testing, updated 4 April 2025. https://www.gov.uk/guidance/monkeypox-diagnostic-testing