Serum Protein Electrophoresis and
Its Diagnostic Significance
Serum contains more than 100 different proteins, each
under separate genetic control. They are transport proteins
for hormones, vitamins, lipids, metals, pigments, and
drugs; enzymes; enzyme inhibitors (proteinase inhibitors);
hormones; antibodies; clotting factors; complement com-
ponents; and kinin precursors. Quantitation (by radial
methods, enzyme-linked immunological methods, and ra-
dioimmunoassay) of the various constituents of serum is of
value in diagnosing and following the course of certain dis-
eases. Several of these proteins are discussed elsewhere in
the text.
A simple and useful technique involves separation
of serum proteins by an electric field at pH
, using
cellulose acetate as a support medium (electrophoresis).
Agarose gel electrophoresis provides a higher resolution
in the separation of proteins than cellulose acetate elec-
trophoresis. The former gives about 12 protein bands and
the latter provides the basic five-band pattern. Separation
of these proteins is possible because each carries different
charges and hence migrates at a differing rate when
subjected to an electric potential. Serum is generally used
instead of plasma because the fibrinogen found in plasma
appears as a narrow band in the
region, which may be
mistaken for the sign of monoclonal paraproteinemia (see
below). The support medium, cellulose acetate, possesses
several advantages over paper: the time required to sepa-
rate the major proteins is short, albumin trailing is absent,
and rapid quantitative determination of protein fractions
by photoelectric scanning (after a suitable staining proce-
dure) is possible. The factors that affect electrophoresis are
ionic strength of the buffer, voltage, temperature, appli-
cation width, and staining.
Figure VI-1 shows normal and some abnormal patterns
of serum protein electrophoresis. The electrophoretic pat-
terns obtained are
indicative of any one disease or
class of disease. Furthermore, a characteristic pattern may
be obscured or not found in a disease entity where nor-
mally such a pattern is expected. Serum electrophoretic
patterns provide only a general impression of the disorder
and require confirmation by other procedures. An alter-
ation (depression or elevation) in a given fraction should
be quantitated by more sensitive and specific methods.
Five major fractions seen in cellulose acetate serum pro-
tein electrophoresis are albumin,
a \
-globulin, a
^-globulin, and /-globulin. Adult reference ranges for
these five fractions, expressed as grams per 100 mL, are
3.2-5.6 for albumin, 0.1-0.4 for ai-globulin, 0.4-0.9
for a
-globulin, 0.5-1.1 for /1-globulin, and 0.5-1
. 6
/-globulin. With the exception of /-globulin, adult values
are attained by 3 months of age for all fractions. Cord blood
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