serum immunoglobulin M level serum total immunoglobulin M level 2014-01-27T13:12:36Z CMO:0002110 The entire amount in a specified sample of serum of all types of immunoglobulin M (IgM), one of the five classes of antibodies produced by the body. IgM is found in circulating body fluids and is the first class of antibodies to appear in response to an initial exposure to an antigen. clinical_measurement_ontology jsmith serum total IgM level true