Overview
This lecture covers the key concepts of hepatitis B serology, including antigen and antibody profiles, their significance, and how to interpret serologic test results for infection, immunity, and transmissibility.
Hepatitis B Antigens
- HBsAg (surface antigen) indicates active hepatitis B infection (acute or chronic).
- HBeAg (envelope antigen) signals active viral replication and high transmissibility.
- HBcAg (core antigen) is present in the virus core but is not detectable in blood.
Hepatitis B Antibodies
- Anti-HBc (antibody to core antigen) appears after infection; IgM for acute, IgG for chronic or past infection.
- Anti-HBs (antibody to surface antigen) indicates immunity (from recovery or vaccination).
- Anti-HBe (antibody to envelope antigen) emerges after envelope antigen declines; signals low transmissibility.
Mnemonics & Key Concepts
- S for "sick": HBsAg means the person is sick with hepatitis B.
- E for "easily spread": HBeAg means easily transmissible infection.
- Anti-HBc means the person has come across hepatitis B (past or ongoing infection).
- Anti-HBs means "anti-sick": represents immunity.
- Antibodies clear antigens from the blood (appearance of antibody = disappearance of corresponding antigen).
Interpreting Serology Patterns
- HBsAg (-), anti-HBc (-), anti-HBs (-): Susceptible, not infected or immune.
- HBsAg (-), anti-HBc (+), anti-HBs (+): Immune due to natural infection.
- HBsAg (-), anti-HBc (-), anti-HBs (+): Immune due to vaccination.
- HBsAg (+), anti-HBc (+), IgM anti-HBc (+), anti-HBs (-): Acute infection.
- HBsAg (+), anti-HBc (+), IgM anti-HBc (-), anti-HBs (-): Chronic infection.
Key Terms & Definitions
- HBsAg — Hepatitis B surface antigen; marker of active infection.
- HBeAg — Hepatitis B envelope antigen; marker of replication and high infectivity.
- HBcAg — Hepatitis B core antigen; not measured in blood tests.
- Anti-HBc — Antibody to core antigen; indicates past or current infection (IgM = acute, IgG = chronic/past).
- Anti-HBs — Antibody to surface antigen; marker of immunity.
- Anti-HBe — Antibody to envelope antigen; marker of low infectivity.
Action Items / Next Steps
- Review serology chart and mnemonics for rapid recall.
- Practice interpreting sample serology results.
- Re-watch the video or review notes as needed for mastery.