Avian Plasma Proteins

The accurate interpretation of avian plasma proteins is very important as a diagnostic tool in avian medicine. Understanding the uses of avian protein electrophoresis will enhance your practice of avian medicine and will help you hone your diagnostic skills. Protein electrophoresis is a practical and useful test in psittacines. Dramatic changes in protein fractions are evident in several diseases, and may help in procuring a diagnosis when other tests are equivocal. Serial electrophoresis is valuable in monitoring response to therapy, as well. We recommend the use of protein electrophoresis as a diagnostic aid in evaluation of the health status of psittacine birds.

At Antech, determination of total plasma proteins is performed by the biuret methodology, which is also known as a colorimetric test. This is regarded as being the most accurate way to measure total avian proteins. Avian total proteins consist of albumin and globulins. All plasma proteins, except immunoglobulins, are manufactured in the liver. Albumin is the largest single fraction in the healthy patient. It serves as the major reservoir of protein, it is the main contributor of colloidal osmotic pressure, it is involved in acid-base balance, and it acts as a transport carrier for small molecules such as vitamins, minerals, hormones and fatty acids. Increases in albumin concentration are associated with dehydration or hemoconcentration. Decreases occur with decreased synthesis (chronic liver disease, dietary protein deficiency or chronic inflammation), increased loss (renal disease, intestinal parasitism or gastrointestinal disease), or sequestration (decreased oncotic pressure or increased hydrostatic pressure). Decreases can also occur with blood loss, severe inanition and chronic infection.

Pre-albumin is a separate and distinct fraction that precedes albumin in electrophoresis. The only known function of this fraction is the transportation of thyroid hormones. Pre-albumin has also been identified in the sera of laying hens, embryonic sera and neonatal sera.

The globulins are composed of three fractions, designated alpha, beta and gamma. In birds, one or two subfractions of the alpha globulin are identified and there is a single fraction for each beta and gamma globulins.

Alpha globulins are a group of proteins manufactured almost entirely by the liver. These proteins usually elevate during the acute phase of inflammatory disease, and therefore are helpful in the diagnosis and monitoring of many infectious diseases and other causes of chronic inflammation. Alpha globulins increase with acute nephritis, severe active hepatitis, active, usually systemic inflammation, malnutrition and in nephrotic syndromes. Decreases can occur with hepatic insufficiency, severe inanition, blood loss and protein-losing GI diseases.

Beta globulins include carrier proteins, complement, ferritin, C-reactive protein, lipoproteins and fibrinogen, and many are also acute phase proteins. In mammals, the beta-2 globulins contain much of the immunoglobulins IgM and IgA, in addition to IgG. Increases in beta globulins occur with acute inflammation, inflammatory liver disease, malnutrition, lipemia artifact, systemic mycotic disease, protein losing enteropathies and the nephrotic syndrome. Decreases occur with hepatic insufficiency, severe inanition, blood loss and protein-losing GI diseases.

Unlike those found in mammals, in birds, the gamma fraction contains most of the immunoproteins, including IgM, IgA, IgE and IgG. Gamma globulins usually elevate with ongoing antigenic stimulation, usually from infectious agents. Broad increases (polyclonal gammopathies) in gamma globulins occur with acute or chronic inflammation, infection, chronic hepatitis and immune mediated disorders. Sharp increases (monoclonal gammopathies) occur with tumors of the reticuloendothelial system and plasma cell dyscrasias. Deficiencies can occur with immunodeficiency states, blood loss, overwhelming infection, protein-losing GI diseases and severe inanition. The half-life of gamma globulins in birds is relatively short. In some species, some nonimmunoglobulin proteins, including transferrin, complement and fibrinogen, are found within the gamma globulins fraction.

Panhypoproteinemia, which occurs when all fractions on the electrophoresis are decreased, occurs with severe inanition or malnutrition, severe hepatic insufficiency, overwhelming infection, protein-losing states (especially GI or kidney), blood loss or third space loss (blood loss into the body cavity or effusion into the body cavity).

There is wide species variation in the accuracy of albumin levels measured by routine wet or dry biochemical methods used on an avian chemistry panel. While generally lower, the albumin levels tend to parallel the results found on protein electrophoresis. Because of this, for the most accurate measurement of albumin, always rely on the electrophoretic results as the most accurate.

Serum proteins include all plasma proteins except the coagulation proteins, principally fibrinogen, which are eliminated by clot separation. In most cases, the difference between avian plasma and avian serum protein concentration is small, and the electrophoretic patterns are not noticeably different between plasma and serum. Since lithium heparinized blood samples are preferred for avian chemistry analysis, this plasma can also be used for protein electrophoresis, although serum can also be used.

Protein electrophoresis has been demonstrated to be a very effective diagnostic tool in avian medicine. Once the total protein level has been determined by the biuret method, the electrophoretic fractions are calculated based on the total protein level.

There are some instances when interpretation of the electrophoretic pattern may be difficult to interpret. Avian neonates and juveniles likely show age-related differences in serum proteins, but this has not been fully investigated. Thus, caution is advised when interpreting electrophoretic patterns in young birds. If possible, age-matched samples from a healthy juvenile of the same species should be run for comparison. In some psittacine species, there may be a monoclonal spike in the beta fraction during periods of egg-laying, when there is a transport of egg proteins to the ovary. This increase in an egg-laying hen has been attributed to transferrin, and to increases in estrogen-induced yolk protein precursors, vitellogenin and lipoproteins. In raptors, there are normal variations that differ from those found in psittacines.

A unique electrophoretic pattern has been reported for acute chlamydiosis. Expect to see a moderate to sever hypoalbuminemia, mild to moderate elevation in beta globulins, and moderate to sever hypergammaglobulinemia. In chronic chlamydiosis, there may be no changes in the inflammatory proteins, or only a mild hyperbetaglobulinemia. In mycotic diseases, especially aspergillosis, expect an increase in the beta fraction during the acute phase. There may be beta or gamma elevations during the chronic phase of aspergillosis. Eventually, chronically infected birds may lose the inflammatory protein response altogether, becoming hypoproteinemic. Mycobacterial infections may show increases in either beta or gamma globulins. Sarcocystis infections usually show an elevation in both beta and gamma fractions. Birds with hepatitis or nephritis often show a decrease in albumin and increases in beta globulins. Gross hemolysis may show a severely restricted (usually gamma) spike composed of hemoproteins that can be misinterpreted.

Avian protein electrophoresis can provide important information that can help the practitioner in diagnosing avian diseases. It is also very helpful in assessing therapy and monitoring progress. Protein electrophoresis is a versatile and simple test that can greatly aid the avian practitioner in avian diagnosis and therapeutic management. The use of this tool in avian diagnostics has both prognostic and therapeutic value.

Cadeusus
Copyright 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
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