HBsAg Screen

What is a HBsAg screening?

HBsAg (hepatitis B surface antigen) screening is a blood test that tells you if you have the hepatitis B virus (HBV). HBsAg is a protein found on the surface of the virus. The test can detect this protein. A positive result on an HBsAg means you have hepatitis B and are contagious.

This screening test is the most common test for hepatitis B virus infection. Reasons you may need this screening include:

• You’re pregnant (you get this test in the first trimester of any pregnancy)
• You’re a doctor, nurse, EMT, police officer or firefighter or work in a job where you’re in contact with blood and bodily fluids
• You’re a teacher or caregiver in a community shelter or correctional facility
• You have risk factors for HBV, like traveling to a country with high rates of hep B, sharing needles or syringes or having multiple sexual partners
• You need hemodialysis due to kidney failure

How does it work?

HBsAg screening is a blood test that tells you if you have a hepatitis B virus infection. Your healthcare provider takes a blood sample from a vein in your arm. Then, they send it to a lab for analysis.

At the lab, the following things happen:

• The test uses antibodies that bind to HBsAg if it’s in your blood sample. This means the antibodies will stick to the virus and/or HBsAg protein in your blood if it’s present.
• If the antibody binds to HBsAg, a light signal goes off on the machine that’s analyzing the blood. This triggers a positive test result. If there’s no signal, the test is negative.
• This is the screen level of HBsAg testing. The automatic reflex test that’s added by the lab is called confirmatory (also known as neutralization) test to ensure the screen result was a true positive.
• If you’ve received a hepatitis B vaccine in the past few weeks, there’s a good chance that your HBsAg test result will be positive. You’ll need to repeat the test in a few weeks.

You don’t need to prepare for the test. You may feel a prick or sting when the needle goes into your vein. A blood draw takes less than five minutes. You can go back to your normal activities after the test.

What are the risks of an HBsAg screen?

There are no risks or side effects to the screening. Like all blood draws, you may have bruising or discomfort at the needle site. This is temporary. The test doesn’t expose you to HBV and isn’t harmful to your health.

When should I know the results?

It can take up to three business days to get your results. Sometimes, you’ll get results within 24 hours. Ask your healthcare provider how long you can expect it to take.

What do the results of an HBsAg screen mean?

A positive or “reactive” confirmatory test result means you have HBV (if not recently vaccinated). The test found the antigen in your blood sample. If your test is negative, you don’t have an active HBV infection.

When should I call my doctor?

Contact your provider if you have questions about your test results. They can explain what your results mean and what comes next for your care.