plasma immunoglobulin measurement blood immunoglobulin M level plasma immunoglobulin M level 2014-01-27T12:36:20Z CMO:0002105 JSmith The amount in a specified sample of plasma of one or more 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 plasma IgM level