a. Multiple Myeloma. It is the most common of the monoclonal gammopathies
and is characterized by neoplastic proliferation of plasma cells or morphologically
abnormal plasma cells (myeloma cells), primarily occurring in the bone marrow. Bone
pain is the most common symptom, with the presence of bone lesions and frequent
bone fractures. SPE shows the presence of a monoclonal hypergammaglobulinemia
while the IEP demonstrates an increase in one of the immunoglobulins, excluding an
increase of IgM. The secretion of Bence Jones protein (light chains, either kappa or
lambda) in the urine is common and diagnostic.
b. Waldenstrom's Macroglobulinemia. This disorder 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. Bone pain and lesions are rare.
c. Heavy Chain Disease. A heterogeneous group of paraprotein disorders
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.
Section V. ENZYME IMMUNOASSAY TECHNIQUES
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.
5-10. TYPES OF ENZYME IMMUNOASSAYS
a. The most widely used assays 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 activity is
measured instead of radioactivity. See the following paragraphs for the meaning of
substrate and conjugate.
b. To measure antibody, antigen is fixed to a solid phase, incubated with test
serum (which contains the antibody to be detected), and then incubated with
anti-human globulin tagged with an enzyme (conjugate). The tagged antihuman
globulin reacts with the antibody being detected. Substrate is then added and the
enzyme activity adherent to the solid phase is then related to the amount of antibody
bound (Figure 5-5).