Immunoglobulin G Subclasses

Approximately 75% of total serum immunoglobulin in adults is IgG, which is divided into four subclasses on the basis of structural differences in the hinge region. IgG3 and IgG1 are closely related, as are IgG2 and IgG4.

Impaired synthesis or abnormal loss may cause deficiencies of immunoglobulins. Primary hypogammaglobulinemias are genetically determined and related to primary B-cell deficiencies. Children with these deficiencies tend to have chronic respiratory infections with severe symptoms. Secondary immunodeficiencies are acquired in conjunction with other immune disorders and seen mainly in adults. Selective IgG subclass deficiencies can occur in spite of a normal total IgG level. Monoclonal increases in one IgG subclass may occur with plasma cell dyscrasias.

Adult reference ranges are:

IgG Subclass

Reference Range (mg/dL)

IgG 1

271 - 1010

IgG 2

104 - 570

IgG 3

14 - 133

IgG 4

4 - 71

Specimen requirement is one plain red top or SST tube of blood.

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