Lecture on Hepatitis B Serology

Introduction

• Lecture by Dirty Medicine
• Focus: Understanding Hepatitis B Serology
• Importance: Frequently appears in practice questions, USMLE, COMLEX

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Hepatitis B Serology: Basics

• Hep B Surface Antigen (HBsAg) (Red): Indicates an active infection.
  • Notation: HB = Hep B, s = Surface, Ag = Antigen
• Hep B Core Antigen (HBcAg) (Blue): Not detectable via serology because it's within the core/capsid.
• Hep B Envelope Antigen (HBeAg) (Green): Indicates active replication & high transmissibility.
  • Produced alongside the core antigen.

Infection Timeline & Antibody Response

• Initial Detection: Surface Antigen & Envelope Antigen.
  • Early markers in blood during infection.
• Body Response: Production of Anti-HBc.
  • First antibody produced in response to core antigen.
  • Types: IgM (acute infection) & IgG (chronic infection).
• Production of Anti-HBe:
  • Antibody that neutralizes envelope antigen.
  • Envelope Antigen Declines as Anti-HBe increases.
• Final Antibody: Anti-HBs:
  • Indicates immunity (from either natural recovery or vaccination).
  • Surface Antigen Declines as Anti-HBs increases.

Antigen and Antibody Functions

• Surface Antigen (HBsAg): Indicates active hep B infection (acute or chronic).
  • Mnemonic: S for Sick
• Envelope Antigen (HBeAg): Indicates replication & high transmissibility.
  • Mnemonic: E for Easily Spread
• Core Antigen (HBcAg): Clinically irrelevant (not detectable).

Antibodies

• Anti-HBc: Previous or ongoing infection.
  • IgM for acute, IgG for chronic
  • Mnemonic: C for Come across Hep B
• Anti-HBe: Low transmissibility
  • Mnemonic: Anti- Spread (opposite of E antigen)
• Anti-HBs: Indicates immunity (natural recovery or vaccination).
  • Mnemonic: Anti-Sick

Understanding Serology Results

• Example 1:
  • HBsAg (-), Anti-HBc (-), Anti-HBs (-)
  • Interpretation: Susceptible (no infection, no immunity)
• Example 2:
  • HBsAg (-), Anti-HBc (+), Anti-HBs (+)
  • Interpretation: Immune due to natural infection (no active infection, past infection, immunity present)
• Example 3:
  • HBsAg (-), Anti-HBc (-), Anti-HBs (+)
  • Interpretation: Immune due to vaccination (no active/past infection, immunity present)
• Example 4:
  • HBsAg (+), Anti-HBc (+), IgM Anti-HBc (+), Anti-HBs (-)
  • Interpretation: Acute infection (active infection, recent infection, no immunity)
• Example 5:
  • HBsAg (+), Anti-HBc (+), IgM Anti-HBc (-), Anti-HBs (-)
  • Interpretation: Chronic infection (active infection, past infection, no immunity)

Conclusion

• Understand the physiological basis
• Use mnemonics to aid memory
• Important for exams (USMLE, COMLEX, etc.)
• Re-watch to reinforce learning
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