Interpreting protein concentrations takes investigative work
Q How does one interpret serum protein concentrations in dogs and cats?
A Alterations in serum protein concentrations are commonly observed in a large number of diseases in dogs and cats. The key types of proteins present in the serum are albumin and globulins. Albumin is the smallest of these proteins, produced only by the liver, and the concentration of albumin molecules in the blood is greater than the concentration of globulin molecules.
As a result, albumin accounts for about 80 percent of the oncotic pressure of the blood. This oncotic pressure prevents water from diffusing from the blood into the tissues. Albumin is also an important carrier protein. Globulins are a heterogeneous group of proteins that are large, but variable in size. Globulins include various types of antibody molecules, other proteins active in the immune system (e.g., complement), clotting factors, many different enzymes and a variety of carrier proteins. Globulins are typically classified as alpha, beta or gamma based on their electrophoretic mobility.Both increased and decreased total protein concentrations are commonly detected abnormalities in dogs and cats. Decreases or increases result from alterations in serum albumin and/or globulin concentrations. In plasma, increased concentration of fibrinogen, a globulin, can occasionally result in increased protein concentration. Interpretation of altered protein concentrations depends on determining which major protein constituents of the serum or plasma (i.e. albumin, globulin, and, in plasma, fibrinogen) are abnormal. Decreased or increased albumin or globulin concentrations do not always result in detectable alterations in the total protein concentration. Thus, albumin and globulin concentrations, as well as total protein concentrations, should be assessed when interpreting alterations.
Causes of decreased or increased total protein, albumin, globulin and fibrinogen concentrations are summarized here.
Investigate the cause
Decreased production of albumin can occur in the disorders highlighted here.
Increased loss of albumin can occur in the following protein-losing disorders:
1) Glomerular disease. Because albumin molecules are smaller than globulin molecules, they leak more readily through damaged glomerular membranes (the net negative charge of albumin molecules as compared to globulin molecules also plays a part in this selective leakage). Severe glomerular disease can result in hypoalbuminemia with a normal to increased serum globulin concentration. Urine protein concentrations and urine protein/creatinine ratios should both be increased with glomerular disease.