Protein Electrophoresis Test Health Article

Description

Proteins are biologically important organic molecules—polymers of amino acids—that contain the elements carbon, hydrogen, nitrogen, and oxygen. Certain proteins may also contain sulfur, phosphorus, iron, iodine, selenium, or other trace elements. There are twenty-two amino acids commonly found in all proteins. The human body is capable of producing fourteen of these amino acids; the remaining eight so-called essential amino acids must be obtained from food. Proteins are found in muscles, blood, skin, hair, nails, and the internal organs and tissues. Enzymes, hemoglobin, and antibodies are proteins, as are many hormones.

Protein mixtures can be fractionated into individual component proteins by a variety of techniques, including precipitation, chromatography, ultracentrifugation, or electrophoresis.

A serum protein electrophoresis test is used to determine the percentage of each protein in the blood by separating them into five distinct classes: albumin, alpha₁-globulin, alpha₂-globulin, beta-globulin, and gamma-globulins (immunoglobulins). High-resolution protein electrophoresis uses a higher current to separate the major proteins comprising the alpha₁-globulin, alpha₂-globulin, and beta-globulin fractions. This procedure produces nine or more bands, including alpha₁ antitrypsin, alpha₂ macroglobulin, haptoglobulin, transferrin, and complement proteins.

In addition to standard protein electrophoresis, the immunofixation electrophoresis test (IFE) may be used to assess the blood levels of specific immunoglobulins. An IFE test is usually ordered if a serum protein electrophoresis test shows an unusually high amount of protein in the gamma-globulin fraction. The IFE tests determine whether the increase in the gamma-globulin fraction is caused by excess immunoglobulins (antibodies), and whether it is polyclonal or monoclonal in nature. Polyclonal increases are caused by infections, allergies, and inflammatory diseases, while monoclonal increases are caused by malignant or benign proliferations of the antibody-producing cells (plasma cells).

Serum proteins

The total serum protein concentration may be used to assess a patient's hydration state: dehydration leads to high total serum protein concentration. Further, the levels of different blood proteins rise or fall in response to such disorders as cancer, intestinal or kidney proteinwasting syndromes, disorders of the immune system, liver dysfunction, impaired nutrition, and chronic fluidretaining conditions.

ALBUMIN. Albumin, which is produced in the liver, is the most abundant blood protein. It makes a major contribution to the osmotic pressure that regulates the movement of water between the tissues and the bloodstream. Albumin binds calcium, thyroid hormones, fatty acids, and many drugs, maintaining them in the circulation and preventing filtration in the kidneys. Low serum albumin levels can be indicative of pathology, and can increase free therapeutic drug levels and decrease total calcium levels. Albumin levels can play a role in the efficacy and toxicity of therapeutic drugs, and in drug interactions.

GLOBULINS. Serum globulins are present in protein electropherograms as four main fractions: alpha₁-, alpha₂-, beta-, and gamma-globulins.

• The major alpha₁-globulin is the "acute-phase" protein alpha₁-antitrypsin, a protease inhibitor produced by the lungs and liver. Alpha₁-antitrypsin deficiency is a marker of an inherited disorder characterized by an increased risk of emphysema.
• Alpha₂-globulins include serum haptoglobin, alpha₂-macroglobulin, and ceruloplasmin. Haptoglobin is an acute-phase protein that binds free hemoglobin released from red blood cells during hemolysis. Haptoglobin binding prevents excretion of free hemoglobin by the kidneys. In addition to hemolysis, low haptoglobin levels can indicate chronic liver disease, tumor metastasis, or severe sepsis. Alpha₂-macroglobulin, a broad-spectrum protease inhibitor, accounts for about one-third of the alpha₂-globulin fraction: its concentration is increased during nephrosis. Ceruloplasmin is an acute-phase protein involved in the storage and transport of copper and iron: its concentration is increased during pregnancy and decreased in Wilson's disease.
• Beta-globulins include transferrin, low-density lipoproteins (LDL), and complement components. Transferrin transports dietary iron to the liver, spleen, and bone marrow. LDL (also referred to as beta lipoprotein) is the major carrier of cholesterol in the blood: high levels are associated with atherosclerosis. Complement is a system of blood proteins required for antibody-mediated cell lysis and involved in the inflammatory response.
• The gamma-globulin fraction contains the immunoglobulins, a family of proteins that function as antibodies. Antibodies, produced in response to infection, allergic reactions, and organ transplants, recognize and bind antigens to facilitate destruction by the immune system. The immune response is regulated by a large number of antigen-specific gamma-globulins that fall into five main classes called IgG, IgA, IgM, IgO, and IgE. Immunoglobulin deficiency due to inherited disorders can range from partial or complete loss of a single immunoglobulin class to complete absence of all immunoglobulins. An abnormally high level of immunoglobulins is generally found in acute and chronic infections, and is an indicator of autoimmune disease. When the serum protein electrophoresis test demonstrates a significant deviation from the normal gammaglobulin levels, an IFE test should be ordered to determine the polyclonal or monoclonal nature of the specific globulin(s) involved.

Quantification of each immunoglobin class and each of the proteins mentioned above may be performed by a procedure called immunonephelometry. This technique uses an antibody specific for the protein to be measured. When the antibody binds to the protein, an immune complex is formed that increases the amount of light scattered by the sample.

Deviations in serum proteins levels from reference levels are considered in conjunction with symptoms and results from other diagnostic procedures.