What does the half-life of Immunoglobulin G (IgG) mean?

Understanding the Half-Life of IgG

The half-life of IgG refers to the time it takes for the concentration of Immunoglobulin G in the bloodstream to decrease by 50%, which is approximately 3-4 weeks (21-30 days) for most IgG subclasses. 1, 2

Clinical Significance of IgG Half-Life

• The half-life of IgG is a critical factor in determining the duration of protection provided by passive immunization with immunoglobulin preparations 1
• Protection from passive immunization typically lasts for at least one half-life of IgG, which is approximately 3 weeks according to the Centers for Disease Control and Prevention 3
• The half-life affects dosing intervals in patients receiving immunoglobulin replacement therapy for primary immunodeficiency diseases 4

IgG Half-Life by Subclass

• IgG1: approximately 29.7 days 2
• IgG2: approximately 26.9 days 2
• IgG3: approximately 15.7 days (notably shorter than other subclasses) 2
• Total IgG: approximately 25.8 days 2

More recent studies have found similar but slightly longer half-lives:

• Total IgG: median of 36.1 days (range 18.5-65.9 days) 4
• IgG subclasses: 26.7-38.0 days 4

Clinical Applications

Passive Immunization Scheduling

• The recommended intervals between administration of antibody-containing products and measles- or varicella-containing vaccines are based on the estimated half-life of 30 days for passively acquired antibody 3
• These intervals are extrapolated from the observed interference with immune response to measles vaccine for 5 months after a dose of 80 mg IgG/kg 3

Immunoglobulin Replacement Therapy

• For patients receiving intravenous immunoglobulin (IVIG) therapy, dosing intervals of 3-4 weeks are common, aligning with the half-life of IgG 4
• Trough IgG levels remain relatively constant when IVIG is administered at these intervals 4
• Specific antibodies within IVIG preparations (such as those against cytomegalovirus, tetanus toxoid, and various pathogens) generally have half-lives similar to total IgG 4, 5

Factors Affecting IgG Half-Life

• Individual variation: Half-lives can be highly variable between patients, ranging from 22 to 96 days in some studies 6
• Serum IgG concentration: Some evidence suggests that patients with higher serum IgG concentrations may have different clearance rates 6
• Disease state: Patients with certain conditions may have altered IgG metabolism 2

Clinical Pitfalls and Considerations

• The half-life of IgG3 is significantly shorter than other subclasses, which may affect protection against certain pathogens where IgG3 is the predominant antibody 2, 5
• When calculating protection periods after passive immunization, clinicians should consider that protection generally lasts for at least one half-life of IgG (approximately 3 weeks) 3, 1
• Dosing intervals for IVIG therapy should account for the half-life to maintain adequate trough levels between infusions 4
• The half-life of specific antibodies within immunoglobulin preparations generally follows that of total IgG, ensuring continued protection against targeted pathogens throughout the dosing interval 5