blood immunoglobulin measurement blood immunoglobulin M level 2014-01-27T12:15:55Z CMO:0002092 EFO:0020466 JSmith The amount in a specified sample of blood 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. blood IgM level clinical_measurement_ontology immunoglobulin M measurement