IgG SUBCLASS DEFICIENCY
Serum IgG comprises four subclassess called igG1, IgG2,IgG3 and IgG4, repectively reflecting the relative abundance of these isotypes in the serum. IgG subclass deficiency is diagnosed on finding a reduction in the serum concentration of IgG subclassess, of more than two standard deviation below the mean value for age, despite the total IgG level being normal. In practice, IgG subclass assays are difficult to standardize due to the lack of an internationally accepted reference preparation. Furthermore, genetic variations that influence serum IgG subclass levels exist among different ethnic groups. Hence, age- and population-related normal ranges are not always available.