Sexual healthPopular
HIV Blood Test
HIV-1 and HIV-2 antibodies, HIV p24 antigen
Guide
When to have an STI blood test after exposure
Blood tests for HIV, syphilis and hepatitis need time after exposure to give a reliable result. This is known as the window period.
| Test | Reliable negative result from |
|---|---|
| HIV (4th generation) | 45 days after exposure |
| Syphilis | 12 weeks after exposure |
| Hepatitis B (surface antigen) | 12 weeks after exposure |
| Hepatitis C (antibodies) | 12 weeks after exposure |
Testing early
You can test sooner for peace of mind, but a negative result taken inside the window period needs repeating once the window has passed.
Exposed to HIV in the last 72 hours?
Go to a sexual health clinic or A&E now and ask about PEP (post-exposure prophylaxis). It can prevent HIV but must be started quickly to work.
What blood tests don’t cover
Chlamydia and gonorrhoea are tested with urine samples or swabs, not blood. NHS sexual health clinics offer free testing for these, often with home kits.
Confidential
Your results are shared only with you, unless you ask us to share them.
Please note: this guide is general information and doesn’t replace advice from your GP. If you feel very unwell, call NHS 111, or 999 in an emergency.
Tests mentioned in this guide
Sexual health
Syphilis Blood Test
RPR, Treponemal antibodies
Sexual health
Hepatitis B Test (Surface Antigen)
Hepatitis B surface antigen (HBsAg)
Sexual health
Hepatitis C Blood Test
Hepatitis C antibodies
More guides
- Do I need to fast before a blood test?
- How long do blood test results take?
- Private blood test vs NHS: which should you choose?
- Understanding your blood test results
- Nervous of needles? How to make your blood test easier
- Which blood test do I need?
- Blood tests for tiredness: what to check
- Blood tests for hair loss and thinning hair
- Cholesterol levels explained
- When to have a hormone blood test
- Blood tests for perimenopause and menopause
Book your blood test
From £55 at our Shirley Road clinic in Croydon. Results usually in 1–3 days, no GP referral.