Accurate measurement and interpretation of plasma protein concentration and electrophoresis are important diagnostic tools in avian medicine. Protein electrophoresis is a practical and useful test in assessing health status of psittacine birds. Dramatic changes in plasma protein fractions are evident in several diseases, and may help in establishing a diagnosis when other tests are equivocal. Serial electrophoresis is valuable in monitoring response to therapy.

Although differences between plasma and serum protein concentration and electrophoresis patterns are small, fibrinogen is virtually nonexistent in serum. As fibrinogen concentration is an important indicator of inflammation, plasma is the preferred sample for these tests. Since lithium heparinized blood samples are preferred for avian chemistry analysis, this plasma can also be used for protein electrophoresis.

At Antech Diagnostics, determination of total plasma proteins is performed by a biuret method. This is regarded as the most accurate way to measure total protein concentration in birds. Albumin concentrations, when measured as part of a chemistry profile, are determined using a wet chemistry dye-binding technique. The accuracy of albumin concentration measured by chemical methods is disputed by the claim that this methodology has no correlation to albumin concentration measured by electrophoresis. To investigate this concern, albumin concentrations were compared using wet chemistry and electrophoresis in 37 birds (25 psittacine and 12 non-psittacine). Although the wet chemistry albumin concentrations tended to be lower, results correlated well with those found on protein electrophoresis (see Figure 1). Thus, while electrophoretic measurement of albumin concentration in birds is considered by some to be the "gold standard", the wet chemistry dye-binding technique provides an accurate assessment of aviamalbumin concentration.

Avian plasma proteins (albumin and globulins), except for immunoglobulins, are manufactured in the liver. Albumin is the largest single plasma protein fraction in the healthy patient. It serves as the major reservoir of protein, is a main contributor of colloidal osmotic pressure, is involved in acid-base balance, and acts as a transport carrier for small molecules such as vitamins, minerals, hormones, fatty acids, and many drugs. Increases in albumin concentration may be an artifact of sample hemolysis or may be due to dehydration or hemoconcentration.

Hypoalbuminemia may be due to 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 plasma protein fraction that precedes albumin on electrophoresis, and is involved in the transportation of thyroid hormones.

The globulins are composed of three fractions, designated alpha, beta and gamma. In birds, one or two subfractions of alpha globulins have been identified as well as a single fraction for each of the beta and gamma globulins.

Alpha globulins are a group of proteins manufactured almost entirely by the liver. As concentrations increase during inflammation, their measurement is helpful in the diagnosis and monitoring of many infectious diseases as well as other causes of acute and chronic inflammation. Alpha globulins increase with acute nephritis, severe hepatitis, active systemic inflammation, malnutrition and in the nephrotic syndrome. Decreases can occur with hepatic insufficiency, severe inanition, blood loss and protein-losing gastrointestinal (GI) diseases. Beta globulins include carrier proteins, complement, ferritin, C-reactive protein, lipoproteins and fibrinogen, and many are also acute phase proteins. Increases in beta globulins occur with acute inflammation, hepatitis, malnutrition, lipemia artifact, systemic mycotic disease, and the nephrotic syndrome. Decreases occur with hepatic insufficiency, severe inanition, blood loss and protein-losing enteropathies.