The most common of the monoclonal gammopathies is multiple myeloma, which is
characterized by neoplastic proliferation of plasma cells or abnormal plasma cells
(myeloma cells), primarily occurring in the bone marrow. Serum protein
electrophoresis (SPE) shows the presence of a monoclonal
hypergammaglobulinemia while the immunoelectrophoresis (IEP) demonstrates an
increase in one of the immunoglobulins.
Waldenstrom's macroglobulinemia is characterized by an increase in the
immunoglobulin IgM and one of the light chains. The associated symptoms are
due to an increase in serum viscosity. Hyperviscosity and sludging of blood may
lead to visual disturbances, neurological symptoms, impaired kidney function, and
congestive heart failure.
Heavy chain disease is characterized by the presence of monoclonal but
incomplete heavy chains without light chains in serum or urine. The heavy chain
involved may be gamma, alpha, or mu with alpha being the most common. The
key to diagnosis is the demonstration of the presence of the heavy chain without
any discernable light chain.
Enzyme immunoassays have emerged as quantitative techniques for detection of
extremely small quantities of antigens, haptens, and antibodies. They all employ
various enzymes linked to either an antigen or antibody to form an enzyme-labeled
tag which can easily be detected by measurement of the enzyme activity.
The most widely used immunoassays are enzyme-linked immunoabsorbent assay
(ELISA) and the enzyme immunoassay (EIA). The principles of ELISA and EIA
tests are similar to those of radioimmunoassay (RIA) technique except enzyme
To measure antibody, antigen is fixed to a solid phase, incubated with test serum,
and then incubated with anti-human globulin tagged with an enzyme (conjugate).
Substrate is then added and the enzyme activity adherent to the solid phase is
then related to the amount of antibody bound.
To measure antigen, antibody is bound to the solid phase, a test solution
containing the antigen is added, and then a second enzyme-labeled antibody
(conjugate) with specificity for the antigen being assayed is added and allowed to
incubate. Substrate is then added and measurement of enzyme activity is related
to the antigen concentration.