Clinical Laboratory - Chemical Pathology and Immunology

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Plasma Protein Analysis

The serum total protein and albumin (and calculated estimate of serum globulin by subtracting albumin from total protein) can be indicators of nutritional status, liver function, and immune function.

Low serum albumin suggests poor protein intake, particularly in a child (kwashiorkor), liver disease with diminished hepatocyte protein synthesis, or loss of albumin with nephrosis (glomerular disease).

Low serum globulin suggests diminished B-lymphocyte function from primary or secondary immunodeficiency states.

The serum protein electrophoresis (SPEP) fractionates the major blood proteins into bands, or regions, that can be quantitated. The regions seen include albumin, alpha (1 and 2),beta and gamma globulins, typically in that order due to size and charge. Each of theses regions represents one or more proteins. For example, the gamma region combines immunoglobulins IgG, IgM, and IgA (tiny amounts of IgE circulate, and virtually no IgD).

The alpha globulin fraction contains proteins that act as carriers of substances in the blood. The major alpha 1 fraction is alpha-1-antitrypsin, a protease inhibitor. Proteins in the alpha 2 fraction include ceruloplasmin, which carries copper, and haptoglobin, which binds free hemoglobin. Alpha-2-macroglobulin is another protease inhibitor also found here.

The beta globulin fraction also contains proteins that act as carriers of substances in the blood. Two such proteins are transferrin, which carries iron, and beta-2 microglobulin, which links with the class 1 MHC molecule. The complement component C3 may contribute as well.

SPEP is often used as a screening procedure for the detection of various pathophysiologic states, such as inflammation, protein loss, monoclonal gammopathies, and other dysproteinemias.

In the example below, there is a broad "polyclonal" increase in the gamma region, representing the typical finding with a chronic inflammatory disease.

In the example below, there is a monoclonal immunoglobulin "spike" typical for multiple myeloma, a neoplasm composed of a clonal proliferation of plasma cells.

Bence-Jones protein that represents excessive light chains can be detected in the urine.

Immunoelectrophoresis may be used to detect, confirm, and then characterize the presence of a monoclonal gammopathy identified by serum protein electrophoresis (SPEP) in patients suspected of having a plasma cell dyscrasia.

Quantitation of immunoglobulins can be obtained to determine specifically if levels of IgG, IgM, and IgA are low or high. For example, immunodeficient states with recurrent infections may be due to decrease in one or more immunoglobulin classes.

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