serum immunoglobulin G level serum immunoglobulin G subclass level 2014-01-27T14:52:10Z CMO:0002114 JSmith The amount in a specified sample of serum of one of the subclasses of immunoglobulin G (IgG), the most abundant class of antibodies found in blood serum and lymph. IgG antibodies are active against bacteria, fungi, viruses, and foreign particles, and trigger action of the complement system. IgG subclasses differ in the structure of their hinge regions. clinical_measurement_ontology serum IgG subclass level serum IgG subtype level serum immunoglobulin G subtype level