Total Protein

Total Serum Protein

Indications for performing this test: This test is included in a standard serum chemistry panel. Total proteins include: albumin, globulin, and fibrinogen.

Serum protein is usually measured by the colorimetric biuret method which is highly specific and accurate in the ranges usually found in serum. Its accuracy falters as the levels fall below 1 g/dl. Refractometry is commonly used in practice to measure serum proteins. This method is also accurate, but subject to interference due to hemolysis or lipemia.

A refractometer can be used to measure levels of any soluble solid. (Above is used to measure sugar in berries.)

Interpretation of Dysproteinemias:

Albumin:

Hyperalbuminemia rarely occurs and is generally secondary to dehydration.

Hypoalbuminemia can be associated with decreased production. Albumin is normally produced by the liver. Possible causes of hypalbuminemia include chronic liver disease, intestinal malabsorption, and malnutrition. Dogs with exocrine pancreatic insufficiency (EPI) are surprisingly able to maintain normal plasma protein levels even when they appear severely malnourished. NOTE: Hypoaluminemia is an insensitive measure of liver function. An animal typically must have a 60-80% loss of function before a decreased serum albumin will be manifested.

Hypoalbuminemia may be caused by increased loss. Albumin can be lost from the body in several ways. Protein losing nephropathies result in the loss of albumin in the urine and it may be detected with a urinalysis. Protein losing enteropathies result in excessive loss of albumin in the gut and this may be diagnosed by using a fecal protein test. In a severely burned animal, albumin may be lost though the disrupted skin. Albumin may be lost to third spaces due to vasculitis. Finally, albumin is lost along with blood in hemorrhage.

Mild hypoalbuminemia may occur due to acute tissue trauma and the activation of the acute phase proteins.

Edema is often a result of hypoalbuminemia. In sheep it can be seen as submandibular edema or "bottle jaw".

Globulin:

The globulin measurement is usually calculated by subtracting the albumin concentration from the total protein concentration. Therefore, false albumin concentrations can alter the globulin concentration.

Hyperglobulinemia may result from either increased globulin production or dehydration. The most common cause of true hyperglobulinemia is probably increased production due to chronic antigenic stimulation. The globulin fraction includes the acute-phase proteins which are produced in response to acute tissue injury. These acute phase proteins include: C-reactive protein, serum amyloid A, haptoglobin, fibrinogen, and coagulation proteins. Immunoglobulins will cause a more marked increase in globulin levels. Some tumor cells (notably plasma cell myelomas and occasionally B cell lymphomas) can produce large amounts of immunoglobulin (a monoclonal gammopathy).

Hypoglobulinemia may be seen in cases of failure of passive transfer in neonates. Depending on the defect, other diseases which cause a deficiency in immunoglobulins will also produce hypoglobulinemia. One example is Severe Combined Immunodeficiency of Arabian foals.

Hypoglobulinemia is also seen when globulins are lost with albumin through hemorrhage, exudation, and protein-losing enteropathies. Globulins may be also decreased in conjunction with decreased albumin when protein synthesis is deficient. An example is malnutrition, including malnutrition due to malabsorption and/or maldigestion. In these cases, the A/G ration is usually normal.

Polyclonal Gammopathy

A/G Ratio: A calculated value that is used to aid in the interpretation of total protein values. The ratio will remain normal if both albumin and globulin have been uniformly altered by processes such as dehydration, malnutrition, malabsorption, dilution, and blood loss due to hemorrhage.

Fibrinogen:

Hyperfibrinogenemia commonly occurs in neoplastic or inflammatory responses. Fibrinogen may be a more sensitive indicator of inflammation and infection than neutrophilia in the horse and the cow.

Hyperfibrinogenemia can also be caused by dehydration, which must be differentiated from a true elevation in fibrinogen. Calculation of the plasma protein/fibrinogen ratio is useful. A PP/F ratio <10 is consistent with a true increase in fibrinogen.

Hypofibrinogenemia is consistent with Disseminated Intravascular Coagulation (DIC). In DIC, all of the clotting factors will be consumed as the clotting cascade rages out of control. Fibrinogen is clotting factor 1.

Disseminated intravascular coagulation results in the formation of numerous fibrin-rich microthrombi which are deposited in the small blood vessels at different sites throughout the body. The kidney is one of the most frequently affected organs.

Click on the image for a larger view

Notice the lacy plaques of fibrin on the heart of this foal with pericarditis.

Click on the image for a larger view

For more information . . .

Veterinary Laboratory Medicine, Duncan, Prasse, and Mahaffey page 115-118.

Veterinary Laboratory Medicine, Interpretation & Diagnosis. Meyer & Harvey, pages 330.