Serum Protein Electrophoresis
Last updated: October 13, 2014
Definition: SPEP measures the major blood proteins, albumin, and globulins.
Method: Because proteins are heterogeneous in surface charge and size, they can be separated electrochemically. In zone electrophoresis, serum is placed on an inert surface such as cellulose acetate and exposed to an electrical current. Different proteins in the serum will move at different rates, thus migrating to different locations where they can be quantified. When proteins are present in normal concentrations, this yields the familiar pattern of SPEP that includes albumin and the globulins (α1, α2, β, and γ). α-Globulins include the acute-phase proteins. Immunoglobulins (IgG, IgA, and IgM) migrate predominantly in the γ-globulin fraction and to a lesser extent in the β fraction (particularly IgM).
Normal Values: Variation may occur between laboratories. Total protein ranges from 6.6 to 7.9 g/dL; albumin, 3.3 to 4.5 g/dL; α1, 0.1 to 0.4 g/dL; α2, 0.5 to 1.0 g/dL; β, 0.7 to 1.2 g/dL; and ϒ, 0.5 to 1.6 g/dL.
Abnormal Findings: Analysis of the individual subfractions on the SPEP may yield important information about several disease states.
Total Protein: A decrease in all protein fractions (which would also be seen as a decrease in total protein on chemistry profile) occurs during massive protein loss, typically from the kidney or gastrointestinal tract. An increase in total protein may result from increases in individual fractions, especially the γ-globulins. Increased protein levels are seen in chronic inflammatory diseases, infections, liver disease, and dehydration.
—Albumin. Decreases in albumin may be seen with renal diseases, particularly those associated with membranous glomerular lesions and resultant proteinuria. In such cases, there may be a compensatory increase in proteins in other fractions. Hypoalbuminemia may also be seen in severe liver disease, reflecting impaired synthetic capacity, and as a result of major dermatologic burns. α1– Antitrypsin constitutes a substantial portion of the α1-globulin fraction of the SPEP; thus, decreases in this fraction may signal a1-antitrypsin deficiency.
—α-Globulins. Various proteins synthesized during the acute-phase response migrate in the a1-globulin fraction; therefore, this fraction increases in patients with inflammatory diseases, infections, or malignancies. Increases in the a2-globulin fraction, which encompasses proteins such as haptoglobin, are commonly seen in patients with hypoalbuminemia, for example, secondary to nephrotic syndrome.
—γ-Globulins. Decreases in -y-globulins reflect decreases in IgG, the immunoglobulin present in largest quantity. Decreases in IgG, or hypogamma-globulinemia, may indicate immunodeficiency of the antibody-mediated component of the immune response. Likewise, increases in the -y-globulin fraction largely reflect increases in serum IgG. When this increase is polyclonal (indicated by a diffuse “hump” on the SPEP), it often reflects a response to infection or an autoimmune disease. When a single clone of B cells produces excess amounts of IgG, as in multiple myeloma, the IgG molecules are identical and thus yield a sharp “spike” on SPEP. The immunoglobulin molecules can be specifically identified by immunoelectrophoresis.
—Other uses: Urine protein electrophoresis is particularly useful in detecting light chains (Bence-Jones proteins) secreted by some myelomas. Electrophoretic analysis of CSF for oligoclonal protein bands is used to support the diagnosis of multiple sclerosis.
Indications: SPEP is frequently used in the evaluation of weight loss, fever of unknown origin, hypoalbuminemia, elevated serum protein, or suspected multiple myeloma malignancy, autoimmune disease, or malnutrition.