What does a high varicella (varicella-zoster virus) Immunoglobulin G (IgG) level indicate?

High Varicella IgG Levels: Clinical Significance and Interpretation

A high varicella-zoster virus (VZV) IgG level indicates immunity to varicella, either from previous natural infection or vaccination, and confirms protection against chickenpox. 1

Understanding Varicella IgG Antibodies

• VZV-specific serum antibody serves as a reliable indicator of protection against chickenpox, regardless of whether immunity was acquired through natural infection or vaccination 1
• The presence of VZV antibodies in serum is generally accepted as evidence of immunity to varicella and protection from chickenpox, though both antibodies and cellular immunity likely work together to provide protection 1
• High sensitivity (100%) has been demonstrated for glycoprotein-based ELISA tests in detecting VZV IgG antibodies in latently infected persons 2

Clinical Significance of High VZV IgG Levels

• Individuals with verified positive VZV IgG levels (except bone marrow transplant recipients) may be considered immune to varicella 3
• High VZV IgG levels indicate that a person has developed immunity either through:
  • Previous natural infection with varicella (chickenpox) 1
  • Successful vaccination against varicella 2
  • Previous herpes zoster (shingles) infection 4

Implications for Patient Management

• Patients with high VZV IgG levels do not require Varicella Zoster Immune Globulin (VZIG) prophylaxis after exposure to varicella 3
• Individuals with high VZV IgG are considered protected and do not need post-exposure prophylaxis even if they become immunocompromised later in life (unless they are bone marrow transplant recipients) 3
• Bone marrow transplant recipients are an exception and should be considered non-immune regardless of previous history of varicella or vaccination status, until they develop varicella or herpes zoster after transplantation 3

Special Considerations

• Patients receiving monthly high-dose immune globulin intravenous (IGIV) (>400 mg/kg) are likely protected against varicella if the last dose was administered less than 3 weeks before exposure 3
• Recent advances in testing include lateral flow immunochromatographic assays that can detect VZV IgG in fingerstick blood with high sensitivity (99.26%) compared to traditional ELISA methods 5
• VZV IgG levels may rise in previously immune individuals after household exposure to varicella, indicating an anamnestic immune response 4

Practical Applications

• VZV IgG testing is useful for:
  • Determining immunity status before potential exposure 1
  • Evaluating the persistence of immunity after vaccination 1
  • Assessing whether waning of vaccine-induced immunity occurs 1
  • Confirming protection in high-risk individuals 1

Limitations

• While high VZV IgG levels indicate immunity, the specific antibody level required for protection is not well defined 1
• Various testing methods have different sensitivity and specificity profiles; glycoprotein-based ELISAs generally show higher sensitivity than whole antigen extract tests 2
• Immunocompromised patients may have detectable antibodies but still be at risk for breakthrough disease due to impaired cellular immunity 1, 6