Electrophoresis is a technique used to separate different elements (fractions) of a blood sample into individual components. Serum protein electrophoresis (SPEP) is a screening test that measures the major blood proteins by separating them into five distinct fractions: albumin, alpha1, alpha2, beta, and gamma proteins. Protein electrophoresis can also be performed on urine.
Purpose
Protein electrophoresis is used to evaluate, diagnose, and monitor a variety of diseases and conditions. It can be used for these purposes because the levels of different blood proteins rise or fall in response to such disorders as cancer, intestinal or kidney protein-wasting syndromes, disorders of the immune system, liver dysfunction, impaired nutrition, and chronic fluid-retaining conditions.
Precautions
Certain other diagnostic tests or prescription medications can affect the results of SPEP tests. The administration of a contrast dye used in some other tests may falsely elevate protein levels. Drugs that can alter results include aspirin, bicarbonates, chlorpromazine (Thorazine), corticosteroids, isoniazid (INH), and neomycin (Mycifradin).
Description
Proteins are major components of muscle, enzymes, hormones, hemoglobin, and other body tissues. Proteins are composed of elements that can be separated from one another by several different techniques: chemical methods, ultracentrifuge, or electrophoresis. There are two major types of electrophoresis: protein electrophoresis and immunoelectrophoresis. Immunoelectrophoresis is used to assess the blood levels of specific types of proteins called immunoglobulins. An immunoelectrophoresis test is usually ordered if a SPEP test has a "spike," or rise, at the immunoglobulin level. Protein electrophoresis is used to determine the total amount of protein in the blood, and to establish the levels of other types of proteins called albumin, alpha1 globulin, alpha2 globulin, and beta-globulin.
Blood proteins
ALBUMIN. Albumin is a protein that is made in the liver. It helps to retain elements like calcium, some hormones, and certain drugs in the circulation by binding to them to prevent their being filtered out by the kidneys. Albumin also acts to regulate the movement of water between the tissues and the bloodstream by attracting water to areas with higher concentrations of salts or proteins.
GLOBULINS. Globulins are another type of protein, larger in size than albumin. They are divided into three main groups: alpha, beta, and gamma.
Alphaglobulins. These proteins include alpha1 and alpha2 globulins. Alpha1 globulin is predominantly alpha1-antitrypsin, an enzyme produced by the lungs and liver. Alpha2 globulin, which includes serum haptoglobin, is a protein that binds hemoglobin to prevent its excretion by the kidneys. Various other alphaglobulins are produced as a result of inflammation, tissue damage, autoimmune disorders, or certain cancers.
Betaglobulins. These include low-density substances involved in fat transport (lipoproteins), iron transport (transferrin), and blood clotting (plasminogen and complement).
Gammaglobulins. All of the gammaglobulins are antibodies—proteins produced by the immune system in response to infection, allergic reactions, and organ transplants. If serum protein electrophoresis has demonstrated a significant rise at the gammaglobulin level, immunoelectrophoresis is done to identify the specific globulin that is involved.
Electrophoretic measurement of proteins
All proteins have an electrical charge. The SPEP test is designed to make use of this characteristic. There is some difference in method, but basically the sample is placed in or on a special medium (e.g., a gel), and an electric current is applied to the gel. The protein particles move through the gel according to the strength of their electrical charges, forming bands or zones. An instrument called a densitometer measures these bands, which can be identified and associated with specific diseases. For example, a decrease in albumin with a rise in the alpha2 globulin usually indicates an acute reaction of the type that occurs in infections, burns, stress, or heart attack. On the other hand, a slight decrease in albumin, with a slight increase in gammaglobulin, and a normal alpha2 globulin is more indicative of a chronic inflammatory condition, as might be seen in cirrhosis of the liver.
Protein electrophoresis is performed on urine samples to classify kidney disorders that cause protein loss. Here also certain band patterns are specific for disease. For example, the identification of a specific protein called the Bence Jones protein (by performing the Bence Jones protein test) during the procedure suggests multiple myeloma.
Preparation
The serum protein electrophoresis test requires a blood sample. It is not necessary for the patient to restrict food or fluids before the test. The urine protein electrophoresis test requires either an early morning urine sample or a 24-hour urine sample according to the physician's request. The doctor should check to see if the patient is taking any medications that may affect test results.
Risks
Risks posed by the blood test are minimal but may include slight bleeding from the puncture site, fainting or lightheadedness after the blood is drawn, or the development of a small bruise at the puncture site.
Normal results
The following values are representative, although there is some variation among laboratories and specific methods. These values are based on the agarose system.
Gammaglobulin levels are increased in chronic inflammatory disease (for example, rheumatoid arthritis, systemic lupus erythematosus); cirrhosis; acute and chronic infection; and a cancerous disease characterized by uncontrolled multiplication of plasma cells in the bone marrow (multiple myeloma). Gammaglobulins are decreased in a variety of genetic immune disorders, and in secondary immune deficiency related to steroid use, leukemia, or severe infection.
Jacobs, David S., et al. Laboratory Test Handbook. 4th ed. New York: Lexi-Comp Inc., 1996.
Pagana, Kathleen Deska. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby, Inc., 1998.
Janis O. Flores
KEY TERMS
Albumin—A blood protein that is made in the liver and helps to regulate water movement in the body.
Electrophoresis—A technique for separating various blood fractions by running an electric current through a gel containing a blood sample.
Globulins—A group of proteins in blood plasma whose levels can be measured by electrophoresis in order to diagnose or monitor a variety of serious illnesses.
Haptoglobin—A protein in blood plasma that binds hemoglobin.
Immunoglobulins—Any of several types of globulin proteins that function as antibodies.
