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Understanding and Interpreting Serum Protein Electrophoresis THEODORE X

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Understanding and Interpreting Serum Protein Electrophoresis THEODORE X. O’CONNELL, M.D., TIMOTHY J. HORITA, M.D., and BARSAM KASRAVI, M.D. Kaiser Permanente Woodland Hills Family Medicine Residency Program, Woodland Hills, California Serum protein electrophoresis is used to identify patients with multiple myeloma and other serum protein disorders. Electrophoresis separates proteins based on their physical proper- ties, and the subsets of these proteins are used in interpreting the results. Plasma protein levels display reasonably predictable changes in response to acute inflammation, malignancy, trauma, necrosis, infarction, burns, and chemical injury. A homogeneous spike-like peak in a focal region of the gamma-globulin zone indicates a monoclonal gammopathy. Monoclonal gammopathies are associated with a clonal process that is malignant or potentially malignant, including mul- tiple myeloma, Waldenström’s macroglobulinemia, solitary plasmacytoma, smoldering multiple myeloma, monoclonal gammopathy of undetermined significance, plasma cell leukemia, heavy chain disease, and amyloidosis. The quantity of M protein, the results of bone marrow biopsy, and other characteristics can help differentiate multiple myeloma from the other causes of monoclonal gammopathy. In contrast, polyclonal gammopathies may be caused by any reac- tive or inflammatory process. (Am Fam Physician 2005;71:105-12. Copyright© 2005 American Academy of Family Physicians.) See page 27 for levels-of- erum protein electrophoresis is a lab- Several subsets of serum protein electro- evidence definitions. oratory examination that commonly phoresis are available. The names of these is used to identify patients with mul- subsets are based on the method that is used tiple myeloma and other disorders of to separate and differentiate the various S serum protein. Many subspecialists include serum components. In zone electrophoresis, serum protein electrophoresis screening in for example, different protein subtypes are the initial evaluation for numerous clinical placed in separate physical locations on a conditions. Sometimes, however, the results gel made from agar, cellulose, or other plant of this examination can be confusing or dif- material.2,3 The proteins are stained, and ficult to interpret. their densities are calculated electronically This article provides a comprehensive to provide graphical data on the absolute review of serum protein electrophoresis, in- and relative amounts of the various proteins. cluding a discussion of how the examination Further separation of protein subtypes is is performed, what it measures, and when it achieved by staining with an immunologi- is indicated. The article also provides a sim- cally active agent, which results in immuno- ple guide to result interpretation and sugges- fluorescence and immunofixation. tions on follow-up of abnormal results. Components of Serum Protein Definitions Electrophoresis Electrophoresis is a method of separating The pattern of serum protein electrophore- proteins based on their physical proper- sis results depends on the fractions of two ties. Serum is placed on a spe- major types of protein: albumin and globu- The pattern of serum pro- cific medium, and a charge is lins. Albumin, the major protein component tein electrophoresis results applied. The net charge (posi- of serum, is produced by the liver under depends on the fractions of tive or negative) and the size normal physiologic conditions. Globulins two major types of protein: and shape of the protein com- comprise a much smaller fraction of the albumin and globulins. monly are used in differentiat- total serum protein content. The subsets of ing various serum proteins.1 these proteins and their relative quantity are January 1, 2005 ◆ Volume 71, Number 1 www.aafp.org/afp American Family Physician 105 Downloaded from the American Family Physician Web site at www.aafp.org/afp. Copyright© 2005 American Academy of Family Physicians. For the private, noncommercial use of one individual user of the Web site. All other rights reserved. Contact [email protected] for copyright questions and/or permission requests. Albumin Beta Alpha1 Alpha2 Gamma Figure 1. Typical normal pattern for serum protein electrophoresis. the primary focus of the interpretation of albumin level is decreased under circum- serum protein electrophoresis.1,3 stances in which there is less production Albumin, the largest peak, lies closest to the of the protein by the liver or in which positive electrode. The next five components there is increased loss or degradation of (globulins) are labeled alpha1, alpha2, beta1, this protein. Malnutrition, significant liver beta2, and gamma. The peaks for these com- disease, renal loss (e.g., in nephrotic syn- ponents lie toward the negative electrode, with drome), hormone therapy, and pregnancy the gamma peak being closest to that elec- may account for a low albumin level. Burns trode. Figure 1 shows a typical normal pattern also may result in a low albumin level. for the distribution of proteins as determined Levels of albumin are increased in patients by serum protein electrophoresis. with a relative reduction in serum water (e.g., dehydration). ALBUMIN The albumin band represents the largest ALPHA FRACTION protein component of human serum. The Moving toward the negative portion of the gel (i.e., the negative electrode), the next peaks involve the alpha1 and alpha2 compo- TABLE 1 nents. The alpha1-protein fraction is com- Indications for Serum Protein Electrophoresis prised of alpha1-antitrypsin, thyroid-binding globulin, and transcortin. Malignancy and Suspected multiple myeloma, Waldenström’s acute inflammation (resulting from acute- macroglobulinemia, primary amyloidosis, or related disorder phase reactants) can increase the alpha1- Unexplained peripheral neuropathy (not attributed protein band. A decreased alpha1-protein to longstanding diabetes mellitus, toxin exposure, band may occur because of alpha1-anti- chemotherapy, etc.) trypsin deficiency or decreased production New-onset anemia associated with renal failure or of the globulin as a result of liver disease. insufficiency and bone pain Ceruloplasmin, alpha2-macroglobulin, and Back pain in which multiple myeloma is suspected haptoglobin contribute to the alpha2-protein Hypercalcemia attributed to possible malignancy band. The alpha2 component is increased as (e.g., associated weight loss, fatigue, bone pain, an acute-phase reactant. abnormal bleeding) Rouleaux formations noted on peripheral blood smear BETA FRACTION Renal insufficiency with associated serum protein elevation The beta fraction has two peaks labeled Unexplained pathologic fracture or lytic lesion identified on radiograph beta1 and beta2. Beta1 is composed mostly Bence Jones proteinuria of transferrin, and beta2 contains beta-lipo- protein. IgA, IgM, and sometimes IgG, along Information from references 2 through 4. with complement proteins, also can be iden- tified in the beta fraction. 106 American Family Physician www.aafp.org/afp Volume 71, Number 1 ◆ January 1, 2005 TABLE 2 Characteristic Patterns of Acute-Reaction Proteins Found on Serum Protein Electrophoresis and Associated Conditions or Disorders Increased albumin Increased beta1 or beta2 globulins Dehydration Biliary cirrhosis Decreased albumin Carcinoma (sometimes) Chronic cachectic or wasting diseases Cushing’s disease Chronic infections Diabetes mellitus (some cases) Hemorrhage, burns, or protein-losing Hypothyroidism enteropathies Iron deficiency anemia Impaired liver function resulting from Malignant hypertension decreased synthesis of albumin Nephrosis Malnutrition Polyarteritis nodosa Nephrotic syndrome Obstructive jaundice Pregnancy Third-trimester pregnancy Increased alpha1 globulins Decreased beta1 or beta2 globulins Pregnancy Protein malnutrition Decreased alpha1 globulins Increased gamma globulins Alpha1-antitrypsin deficiency Amyloidosis Increased alpha2 globulins Chronic infections (granulomatous diseases) Adrenal insufficiency Chronic lymphocytic leukemia Adrenocorticosteroid therapy Cirrhosis Advanced diabetes mellitus Hodgkin’s disease Nephrotic syndrome Malignant lymphoma Multiple myeloma Decreased alpha2 globulins Rheumatoid and collagen diseases (connective Malnutrition tissue disorders) Megaloblastic anemia Waldenström’s macroglobulinemia Protein-losing enteropathies Decreased gamma globulins Severe liver disease Agammaglobulinemia Wilson’s disease Hypogammaglobulinemia Information from reference 6. GAMMA FRACTION still is suspected, immunofixation also should Much of the clinical interest is focused on be performed because this technique may be the gamma region of the serum protein spec- more sensitive in identifying a small monoclo- trum because immunoglobulins migrate to nal (M) protein.5 this region. It should be noted that immuno- globulins often can be found throughout the Interpretation of Results electrophoretic spectrum. C-reactive protein Plasma protein levels display reasonably pre- (CRP) is located in the area between the beta dictable changes in response to acute inflam- and gamma components.1 mation, malignancy, trauma, necrosis, infarction, burns, and chemical injury. This Indications so-called “acute-reaction protein pattern” Serum protein electrophoresis commonly involves increases in fibrinogen, alpha1-anti- is performed when multiple myeloma is trypsin, haptoglobin, cerulo- suspected. The examination also should be plasmin, CRP, the C3 portion considered in other “red flag” situations of complement, and alpha1-
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