Why is a distinction made between IgG subclass deficiency and Specific Antibody Deficiency?
Specific antibody deficiency indicates a failure of the immune system to mount a protective antibody response to exposure to an organism, and is typically assessed using vaccine responses. IgG subclasses do not provide the same functional information. There is therefore a need for careful diagnosis and distinction between these two conditions to determine the most appropriate therapeutic regimen. It is now generally agreed that IgG subclass level estimation in serum is a poor predictor of infectious risk and is of limited value in identifying those patients most likely to benefit from IVIg therapy. Many patients with previously diagnosed IgG subclass deficiency and recurrent infection on IVIg may have specific functional antibody deficits. AHMAC 2000 criteria included IgG subclass deficiency at a “Category 1 indication” with the prerequisite that “Failure of antibody response to vaccine antigens” is demonstrated. In practice this important requirement was seldom imposed. Host antibody
