What are serum proteins?
Serum is the liquid portion of blood from which the red blood cells, white blood cells, and factors involved in blood clotting have been removed.
Serum contains a large number of proteins that perform diverse functions. These functions include providing cellular nutrition, defending against infections, playing a role in inflammation, and acting as hormones or enzymes.
The individual proteins have distinctive sizes and electrical charges.
Where are these proteins made?
The liver produces many of these serum proteins. The immune system is also a major source of some proteins.
What is serum protein electrophoresis?
Serum protein electrophoresis involves placing a serum sample onto a semi-solid gel. An electrical current is then applied to this gel, causing the individual proteins within the serum to move along the length of the gel.
The proteins will settle out on the gel in bands, according to their size and electrical charge. The protein bands are then stained with a special dye so that they can be seen. After the gel has dried, a special instrument called a densitometer measures the bands.
The densitometer gives a visual print out or graph of the proteins bands, along with a calculation of the relative percent of the total protein that is from each band. These percentages are compared to reference ranges that have been determined for healthy animals.
Because of the specialized equipment that is necessary for serum protein electrophoresis, this test must be performed at a referral laboratory.
Serum protein electrophoresis is usually only determined if the total protein concentration is found to be significantly increased on routine blood tests (such as the serum chemistry profile).
What are the main serum proteins that are measured by electrophoresis?
In general, protein electrophoresis is not sensitive enough to allow visualization of each of the hundreds of individual proteins that are found in serum. Instead, broad groups of proteins with similar size and electrical charge are measured. The major groups, or fractions, of proteins include alpha, beta, and gamma globulins.
The one individual protein that is distinctly separated by electrophoresis is albumin.
What do changes in these protein groups mean?
Albumin comprises from 35% to 50% of the total serum protein concentration in animals. Albumin has many functions, including the maintenance of normal fluid pressure within the blood vessels (this is termed colloidal osmotic pressure), and the transport of minerals, hormones, and fatty acids within the blood stream. The liver is the site of albumin production. Since over-production of albumin does not occur, only decreases in albumin concentration are of concern. A decreased amount of serum albumin may mean decreased liver production, or increased loss of this protein via hemorrhage, or via loss into the urinary or gastrointestinal tracts.
Proteins comprising the alpha and beta globulin fractions are also predominantly produced in the liver. These alpha and beta fractions include proteins involved in the normal inflammatory response (the so-called acute phase proteins), proteins involved in the transport of lipids, and proteins involved in iron transport.
Significant increases in the alpha and beta fractions are seen primarily with inflammation. However, liver disease, kidney disease and some tumors may also cause increases in these fractions. Significant decreases in the alpha and beta protein fractions are mainly noted with liver disease and are therefore related to decreased production of these proteins.
The final category of proteins seen with protein electrophoresis is the gamma globulin fraction. Specific cells of the immune system, called lymphocytes, produce immunoglobulin (antibodies) in response to material or organisms that are foreign to the body. These antibodies will be found in the gamma globulin fraction.
Increases in the gamma globulin fraction may be seen graphically as broad-based increases or as narrow-based increases. The pattern of increase is suggestive of the type of underlying disease process.
Broad-based increases in the gamma globulin fraction may be seen in response to chronic infections, immune-mediated disease processes, some cancers and certain viral diseases (for example, feline infectious peritonitis).
Narrow-based increases in the gamma globulin fraction are supportive of underlying cancer of the immune system (such as lymphoma and multiple myeloma) as well as some infectious conditions (for example, ehrlichiosis). If clinically warranted, these narrow-based increases can be further characterized by immunoelectrophoresis, a specialized test which definitively identifies the protein components within this fraction and therefore helps to confirm or exclude the possibility of cancer.
Decreases in the gamma globulin fraction are unusual and are typically seen in very young animals that may have not received sufficient colostrum (the first milk containing antibodies) from their mothers
As a rule, these protein fractions do not change in isolation. For example, if there is inflammation of the liver, the albumin fraction may be decreased while the beta and gamma globulin fractions are increased. Therefore, it is important to evaluate the overall pattern of change and relate these findings to your pet's symptoms and other laboratory data.
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