Interpreting Hepatitis B Serology

Introduction

• Presenter: Tom from Zero to Finals
• Focus: Simplifying the understanding of Hepatitis B serology to be easily remembered, crucial for exams and clinical practice.
• Additional Resources: Zero to Finals - Hepatitis

Basic Concept: Antibodies

• Antibodies: Proteins produced by B-cells, each specific to a single protein (antigen).
• Antigen: Protein targeted by antibodies; can be part of viruses, bacteria, fungi, cancers, or body's own cells (autoimmune disease).
• Function: Attach to antigens to help the immune system launch an attack.

Hepatitis B Virus (HBV) Antigens

1. Surface Antigen (HBsAg): Found on the surface of the virus.

   • Presence in blood: Indicates HBV infection.
   • Negative result: No active infection.
   • Role in vaccine: Injected to create immune response, leading to immunity.

2. E Antigen (HBeAg): Found between the core and surface, released during replication.

   • Presence: Indicates active replication and high infectivity during the acute phase.

3. Core Antigen (HBcAg): Found in the virus core, not circulating in blood.

   • Not detectable in blood tests.

Hepatitis B Antibodies

1. Surface Antibody (anti-HBs): Response to the surface antigen.

   • Indicator of previous vaccination or past HBV infection.
   • Need other markers to differentiate cause (vaccine or infection).

2. E Antibody (anti-HBe): Response to the E antigen.

   • Presence: Implies past acute phase, now less infectious.

3. Core Antibody (anti-HBc)

   • Can distinguish between acute, chronic, and past infections.
   • IgM anti-HBc: Indicates acute infection (high titer for acute, low for chronic).
   • IgG anti-HBc: Indicates past infection if HBsAg is negative.

Viral Load Testing

• HBV DNA test: Direct testing for Hepatitis B viral DNA.
  • Counts viral copies in the bloodstream, referred to as viral load.

Screening Recommendations

1. Test for anti-HBc: Indicates previous infection.
2. Test for HBsAg: Indicates active infection.
3. If positive, test for HBeAg: Assess infectivity and replication.
4. Test for HBV DNA: Determine viral load.

Key Reminder

• Positive anti-HBs result: Likely indicates prior vaccination.

Conclusion

• Importance of understanding serology for exams and clinical practice.

• Additional resources available on Zero to Finals website, including notes, illustrations, test questions, and blog.

• Zero to Finals YouTube Channel