What it measures
- Hepatitis B surface antigen (HBsAg)
Testing for a current hepatitis B infection
Hepatitis B is a virus that infects the liver. Many people have no symptoms, especially at first, so testing is the only way to know. HBsAg is part of the virus and is usually detectable within a few weeks of infection.
A positive result means you currently have hepatitis B and should be referred to a liver specialist, as effective treatment and monitoring are available. Your close contacts can be vaccinated.
For a complete picture, this test is often combined with the core antibody test.
Who it’s for
- Possible exposure to hepatitis B
- Being born in, or having lived in, a country where hepatitis B is common
- Occupational or pre-procedure screening
- A partner or family member with hepatitis B
How to prepare
- Drink plenty of water beforehand; it makes the sample quicker and easier to take.
- You don’t need to fast.
Hepatitis B Antigen (HBsAg) Blood Test: your questions
How soon after exposure can I test for hepatitis B?
HBsAg is usually detectable within a few weeks, but it can take up to 3 months. A repeat test at 3 months confirms a negative result.
Information on this page is general and doesn’t replace advice from your GP, midwife or consultant. If you feel unwell or are worried about symptoms, contact your GP, call NHS 111 or, in an emergency, 999.