Hepatitis B Surface Antigen (HBsAg)
- Sample Type
- Serum
- Fasting
- No
- Unit
- Index
Function
The Hepatitis B Surface Antigen (HBsAg) test is the earliest immunological marker of an acute Hepatitis B virus (HBV) infection. HBsAg is a protein found on the surface of the virus; its presence in the blood indicates that the person is currently infected and can pass the virus to others.
Why it is Ordered
This test is the primary screening tool for HBV. It is ordered for individuals with elevated liver enzymes (ALT/AST), those who have been exposed to blood or body fluids of an infected person, pregnant women (to prevent mother-to-child transmission), and individuals in high-risk groups. It is also used to monitor the status of chronic HBV patients.
Associated Conditions
- Acute Hepatitis B: The initial stage of infection. If HBsAg persists for more than six months, the infection is classified as chronic.
- Chronic Hepatitis B: A long-term infection that can lead to significant liver damage, including cirrhosis and hepatocellular carcinoma (liver cancer).
- Carrier Status: Some individuals remain HBsAg positive without active liver inflammation, but they remain infectious to others.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
A 'false reactive' result can occur shortly after receiving a Hepatitis B vaccination (typically within 1-2 weeks). Conversely, in rare 'occult' Hepatitis B cases, HBsAg may be negative even if the virus is present in the liver, requiring HBV-DNA PCR testing for confirmation.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Hepatitis B Surface Antigen (HBsAg):
Official Sources
Research & Guidelines
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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