What Does Being HBsAg Positive Mean?

An HBsAG test is done to check for active or chronic hepatitis B

Hepatitis B surface antigen (HBsAg) is a protein that appears in the blood when you have a hepatitis B infection. An HBsAg blood test can detect this antigen. If you're positive, it means you have the virus and can pass it to others through your blood or body fluids.

The HBsAg test is used along with other tests to confirm hepatitis B and whether or not you're contagious.

What Is Hepatitis B?

Hepatitis B is a serious liver infection caused by the hepatitis B virus (HBV). For some people, hepatitis B infection becomes chronic, meaning it lasts more than six months. Having chronic hepatitis B increases your risk of developing liver failure, liver cancer or cirrhosis—a condition that causes permanent scarring of the liver.

Most people infected with hepatitis B as adults recover fully, even if their signs and symptoms are severe. Infants and children are more likely to develop a chronic hepatitis B infection.

Is Being HBsAg Positive a Curable Condition?

No, at least not yet as researchers continue to study hepatitis B. An HBsAg positive test confirms the infection. A vaccine can prevent hepatitis B, and you can recover from infection, but there's no cure if you have it. However, certain precautions can help you to prevent the spread of HBV.

Hepatitis B Symptoms

symptoms of hepatitis

Verywell / Brianna Gilmartin

Signs and symptoms of hepatitis B, ranging from mild to severe, usually appear about one to four months after you've been infected. They may include:

  • Abdominal pain
  • Dark urine
  • Fever
  • Joint pain
  • Loss of appetite
  • Nausea and vomiting
  • Weakness and fatigue
  • Yellowing of your skin and the whites of your eyes (jaundice)

Hepatitis B Causes

The hepatitis B virus is passed from person to person through blood, semen, or other body fluids.

With a positive HBsAg, transmission routes for infection include:

  • Sexual contact: You may become infected if you have unprotected sex with an infected partner whose blood, saliva, semen, or vaginal secretions enter your body.
  • Sharing of needles: HBV is easily transmitted through needles and syringes contaminated with infected blood. Sharing intravenous (IV) drug paraphernalia puts you at high risk of hepatitis B.
  • Accidental needle sticks: Hepatitis B is a concern for healthcare workers and anyone else who comes in contact with human blood.
  • Mother to child: People who are pregnant and are infected with HBV can pass the virus to their babies during childbirth. However, the newborn can be vaccinated to avoid getting infected in almost all cases. Talk to your healthcare provider about being tested for hepatitis B if you are pregnant or want to become pregnant.

What Is HBsAg?

HBsAg is cleared within four to six months in self-limited infections (infections that resolve by themselves). It can be detected in the blood during both acute infections (infections that come on suddenly) and chronic infections (infections that last for longer than six months).

Along with levels of HBsAg, symptoms of the individual, and other factors, there are additional antibodies that can be tested to distinguish between acute and chronic infections.

At the center of the hepatitis B virus is DNA, which contains the genes the virus uses to replicate itself. Surrounding the DNA is a protein called hepatitis B core antigen (HBcAG), which cannot be detected with blood tests.

Surrounding this is HBsAg, which is actually part of the "envelope" that protects the virus from attack by the body's immune system. However, the immune system is good at getting through this envelope in order to kill the virus. When it does, remnants of surface antigen protein are left in the blood-like debris, which lab tests can detect.

Your body can produce antibodies to any of these antigens once you are exposed to the virus. These antibodies develop at different stages of the infection.

If you receive a vaccination for hepatitis B, you will develop antibodies to protect you from hepatitis B infection. The HBsAg protein in the vaccine is manufactured by modified yeast cultures, so it is safe from transmission of hepatitis.

Screening Tests for Hepatitis B

Your blood may be screened for HBV for many different reasons. There are several types of test, but the three generally included are the HBsAg, the antibody to HBsAg (also called HBsAb), and the antibody to hepatitis B core antigen (HBcAb).

These tests allow the healthcare provider to know whether you could benefit from vaccination, or if you have active or chronic hepatitis B and need counseling, care, or treatment.

You may be routinely screened if you are pregnant, are donating blood or tissue, need immunosuppressive therapy, or have end-stage renal disease. You will also be screened if you are in groups that are at higher risk for HBV.

HBsAg Normal Range

The HBsAg test focuses on the presence or absence of this biomarker. As such, it's more important to know if you are HBsAg positive or negative rather than focus on a "normal" result. Test kits typically measure a range of between 0.05 to 250 international units per milliliter (IU/ml), though some results may be higher. The HBsAg levels then correlate to your status as someone who's not exposed, who has been vaccinated or is in a recovery stage of an infection, or who is in a currently active state of infection.

Frequently Asked Questions

  • Why do you get an HBsAg test when you’re pregnant?

    Mothers can pass hepatitis B to their babies during delivery. An HBsAg test is done during pregnancy so that steps can be taken to avoid infecting the baby as it is born, if needed.

  • What’s the difference between positive HBsAg and HBsAb tests?

    An HBsAg test checks whether you currently have a hepatitis B infection and, therefore, are infectious. An HBsAb test checks to see if you’re protected against hepatitis B, which is usually due to vaccination or having recovered from the virus.

  • How is HBsAg positive treated?

    There is no specific treatment for acute HBV infections. The World Health Organization recommends antiviral medication for chronic infection, with Viread (tenofovir) or Baraclude (entecavir) considered the strongest oral antiviral drugs. 

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Steyn L. Love your liver. Professional Nursing Today. 2018;22(4):21-4.

  2. Seto WK, Lo YR, Pawlotsky JM, Yuen MF. Chronic hepatitis B virus infection. Lancet. 2018 Nov 24;392(10161):2313-24. doi:10.1016/S0140-6736(18)31865-8

  3. Centers for Disease Control and Prevention. Hepatitis B questions and answers for the public.

  4. U.S. Department of Health and Human Services, Office of Population Affairs. Hepatitis B.

  5. Wilkins T, Sams R, Carpenter M. Hepatitis B: screening, prevention, diagnosis, and treatment. Am Fam Physician. 2019;99(5):314-323.

  6. Hepatitis B Foundation. Hepatitis B Blood Tests.

  7. Karra VK, Chowdhury SJ, Ruttala R, Polipalli SK, Kar P. Clinical Significance of Quantitative HBsAg Titres and its Correlation With HBV DNA Levels in the Natural History of Hepatitis B Virus Infection. J Clin Exp Hepatol. 2016 Sep;6(3):209-215. doi:10.1016/j.jceh.2016.07.002.

  8. Screening for hepatitis b virus infection in pregnant women: recommendation statement. AFP. 2020;101(2):112-114.

  9. World Health Organization. Hepatitis B.

Additional Reading

By Charles Daniel
 Charles Daniel, MPH, CHES is an infectious disease epidemiologist, specializing in hepatitis.