serum immunoglobulin M level serum autoantibody level serum immunoglobulin M-type rheumatoid factor level 2014-11-10T12:17:32Z CMO:0002609 The amount in a specified sample of serum of rheumatoid factor that is expressed as an immunoglobulin M (IgM) molecule. Rheumatoid factor (RF) is an autoantibody against the Fc portion of IgG found in rheumatoid arthritis and some other autoimmune diseases. RF and IgG join to form immune complexes that contribute to the disease process. clinical_measurement_ontology jsmith serum IgM-RF level serum IgM-rheumatoid factor level