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What is Hepatitis B Surface Antigen (HBsAg)?

Hepatitis B Surface Antigen (HBsAg) is a protein found on the surface of the hepatitis B virus. When someone is infected with hepatitis B, this antigen is present in their blood and can be detected through laboratory testing. The HBsAg screen is the primary blood test used to determine if a person has an active hepatitis B infection, whether acute (short-term) or chronic (long-term). This test detects the presence of the antigen itself rather than antibodies produced by the immune system, making it a direct indicator of current infection.

Why is HBsAg important?

Hepatitis B is a serious liver infection caused by the hepatitis B virus that can lead to acute illness, chronic infection, liver damage, cirrhosis, liver cancer, and even death. The World Health Organization estimates that approximately 254 million people worldwide live with chronic hepatitis B infection. Early detection through HBsAg screening is critical because many people with hepatitis B have no symptoms, especially in the early stages or with chronic infection.
HBsAg screening is particularly important for certain populations, including pregnant women (to prevent transmission to newborns), healthcare workers, people with multiple sexual partners, injection drug users, and individuals from regions where hepatitis B is common. A positive HBsAg result indicates that the person is infected and can transmit the virus to others through blood, semen, or other body fluids. Early identification allows for appropriate medical monitoring, antiviral treatment when necessary, and preventive measures to protect others from infection.
If HBsAg remains detectable for more than six months, it indicates chronic hepatitis B infection, which requires ongoing medical management to monitor liver health and prevent complications.

How can I better understand my HBsAg levels?

HBsAg Screen Results:

  • Negative (Non-reactive): No hepatitis B surface antigen detected. This indicates no current hepatitis B infection.
  • Positive (Reactive): Hepatitis B surface antigen detected. This indicates active hepatitis B infection (acute or chronic).

The HBsAg test is typically reported as simply positive or negative. A negative result means no active hepatitis B infection is present. A positive result means the virus is present in the blood and the person is infectious. Additional testing is usually performed following a positive HBsAg result to determine whether the infection is acute or chronic, assess liver function, and guide treatment decisions.
If you test positive for HBsAg, your healthcare provider will likely order follow-up tests including hepatitis B e-antigen (HBeAg), hepatitis B core antibody (anti-HBc), and hepatitis B viral load to better characterize your infection. Testing will be repeated after six months because if HBsAg persists beyond this timeframe, it indicates chronic infection requiring long-term management.

How can I maintain optimal liver health and prevent hepatitis B?

If you test negative for HBsAg and want to prevent hepatitis B infection, consider the following strategies:
Vaccination: The hepatitis B vaccine is the most effective way to prevent infection. The vaccine series typically consists of three or four shots given over six months and provides long-lasting protection. Vaccination is recommended for all infants, unvaccinated children and adolescents, and adults at increased risk.
Safe Practices: Hepatitis B spreads through contact with infected blood and body fluids. Practice safe sex by using condoms, avoid sharing needles or personal items like razors or toothbrushes, and ensure any tattoos or piercings are done with sterile equipment at reputable establishments.
For Those with Chronic Hepatitis B: If you test positive for HBsAg and have chronic infection, work closely with a hepatologist or infectious disease specialist. Antiviral medications can help control the virus and reduce liver damage. Avoid alcohol, maintain a healthy weight, and get regular monitoring of liver function. Inform sexual partners and household members so they can get tested and vaccinated if needed.

Where can I learn more?

DISCLAIMER: This information is for educational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider for interpretation of your urine albumin results and for personalized kidney health recommendations.