Determination of protein fractions in blood serum (albumin, α-1-globulin, α-2-globulin, β-globulin, γ-globulin, A/G ratio)
Why this test?
To assess the qualitative and quantitative ratio of the main protein fractions in patients with acute and chronic infectious diseases, autoimmune conditions and some diseases of the liver (chronic viral hepatitis) and kidneys (nephrotic syndrome).
For diagnosis and control of treatment of monoclonal gammopathy (multiple myeloma and monoclonal gammopathy of unclear genesis).
For the diagnosis of immunodeficiency syndromes (Bruton's agammaglobulinemia).
In what cases is it prescribed?
When examining a patient with acute or chronic infectious diseases, autoimmune conditions and some diseases of the liver (chronic viral hepatitis) and kidneys (nephrotic syndrome).
With symptoms of multiple myeloma: pathological fractures or bone pain, unmotivated weakness, persistent fever, recurrent infectious diseases.
Abnormalities in other laboratory tests that suggest multiple myeloma: hypercalcemia, hypoalbuminemia, leukopenia, and anemia.
If alpha-1-antitrypsin deficiency is suspected, Bruton's disease and other immunodeficiencies.
The total serum protein includes albumin and globulins, which are normally in a certain qualitative and quantitative ratio. It can be assessed using several laboratory methods. Electrophoresis of proteins in an agarose gel is a method of separating protein molecules, based on the different speed of their movement in an electric field depending on size, charge and shape. When dividing the total protein of blood serum, it is possible to identify 5 main fractions. During electrophoresis, protein fractions are determined in the form of bands of different widths with a characteristic, specific for each type of protein location in the gel. To determine the share of each fraction in the total amount of protein, the intensity of the bands is evaluated. So, for example, the main protein fraction of serum is albumin. It accounts for about 2/3 of all blood protein. Albumin corresponds to the most intense band obtained during electrophoresis of blood serum proteins of a healthy person. Other serum fractions detected by electrophoresis include: alpha-1 (mainly alpha-1-antitrypsin), alpha-2 (alpha-2-macroglobulin and haptoglobin), beta (transferrin and C3 component of complement) and gamma - globulins (immunoglobulins). Various acute and chronic inflammatory processes and tumor diseases are accompanied by a change in the normal ratio of protein fractions. The absence of any band may indicate a protein deficiency observed in immunodeficiencies or alpha-1-antitrypsin deficiency. An excess of any protein is accompanied by an increase in the intensity of the corresponding band, which is most often observed in various gammapathies. The result of electrophoretic separation of proteins can be presented graphically, while each fraction is characterized by a certain height, which reflects its share in the total serum protein. A pathological increase in the share of any fraction is called a peak, for example, M-peak in multiple myeloma.
The study of protein fractions plays a special role in the diagnosis of monoclonal gammopathy. This group of diseases includes multiple myeloma, monoclonal gammopathy of unclear origin, Waldenström's macroglobulinemia, and some other conditions. These diseases are characterized by clonal proliferation of B-lymphocytes or plasma cells, in which uncontrolled production of one type of immunoglobulin occurs. When separating the serum protein of patients with monoclonal gammopathy using electrophoresis, characteristic changes are observed - the appearance of a narrow intense band in the area of gamma globulins, which is called M-peak, or M-protein. M-peak can reflect the hyperproduction of any immunoglobulin (both IgG in multiple myeloma, and IgM in Waldenström's macroglobulinemia and IgA in monoclonal gammopathy of unclear origin). It is important to note that the method of electrophoresis in agarose gel does not allow different classes of immunoglobulins to be differentiated from each other. For this purpose, immunoelectrophoresis is used. In addition, this study makes it possible to give an approximate estimate of the amount of pathological immunoglobulin. In this regard, the study is not indicated for the differential diagnosis of multiple myeloma and monoclonal gammopathy of unclear origin, as it requires a more accurate measurement of the amount of M-protein. On the other hand, if the diagnosis of multiple myeloma has been verified, the method of electrophoresis in an agarose gel can be used to evaluate the dynamics of M-protein during treatment control. It should be noted that 10% of patients with multiple myeloma do not have any abnormalities in the proteinogram. Thus, a normal proteinogram obtained by electrophoresis in an agarose gel does not completely rule out this disease.
Another example of gammopathy, which is determined by electrophoresis, is its polyclonal variety. It is characterized by hyperproduction of various types of immunoglobulins, which is defined as a homogeneous increase in the intensity of the gammaglobulin band in the absence of any peaks. Polyclonal gammopathy is observed in many chronic inflammatory diseases (infectious and autoimmune), as well as in liver pathology (viral hepatitis).
Research of protein fractions of blood serum is used to diagnose various immunodeficiency syndromes. An example can be Bruton's agammaglobulinemia, in which the concentration of all classes of immunoglobulins decreases. Electrophoresis of serum proteins of a patient with Bruton's disease is characterized by the absence or extremely low intensity of the gammaglobulin band. Low intensity of the alpha-1 band is a characteristic diagnostic sign of alpha-1-antitrypsin deficiency.
A wide range of conditions in which qualitative and quantitative changes in the proteinogram are observed include a wide variety of diseases (from chronic heart failure to viral hepatitis). Despite the presence of some typical deviations of the proteinogram, which in some cases make it possible to diagnose the disease with complete confidence, usually the result of electrophoresis of serum proteins cannot serve as an unequivocal criterion for making a diagnosis. Therefore, the interpretation of the study of protein fractions of blood is carried out taking into account additional clinical, laboratory and instrumental data.