Serum protein electrophoresis analyzes the proteins present in the fluid portion of the blood, known as serum. This laboratory procedure separates these proteins into distinct groups, providing a quantitative snapshot of their relative concentrations. Analyzing this protein profile helps healthcare providers diagnose, monitor, and manage a wide range of conditions, including cancers, liver and kidney disorders, and immune system abnormalities.
How Electrophoresis Separates Serum Proteins
The separation of serum proteins is achieved through electrophoresis, which relies on the movement of charged molecules within an electric field. A small sample of serum is applied to a supporting medium, such as an agarose gel or cellulose acetate membrane, soaked in a buffer solution to maintain a stable pH. An electric current is then passed through the medium, causing the proteins to migrate from the application point.
The rate and direction of migration depend primarily on the protein’s net electrical charge, size, and shape. Since most serum proteins carry a negative charge, they move toward the positive electrode (anode). Albumin, being the smallest and most highly negatively charged, moves the fastest and migrates the furthest. Larger, less-charged proteins, such as immunoglobulins, travel slower and remain closer to the starting point. The separated proteins are chemically stained to make them visible as distinct bands. A densitometer scans these bands, converting the stain intensity into a graph with peaks corresponding to the concentration of protein in each fraction.
When Doctors Order This Diagnostic Tool
Physicians order serum protein electrophoresis when initial laboratory results or symptoms suggest a disorder affecting protein production or loss. A common indication is an abnormal result from a routine total protein or albumin test, especially when a large difference between the albumin level and the total protein count suggests an increase in globulin proteins.
The test is frequently used to investigate plasma cell disorders, such as multiple myeloma. Symptoms prompting the test include unexplained chronic bone pain, recurrent infections, anemia, or kidney dysfunction. It is also ordered for unexplained swelling (edema), which may indicate protein loss from the kidneys, or for symptoms of chronic liver disease, which impairs protein synthesis. Furthermore, it helps monitor patients with chronic inflammatory conditions or autoimmune disorders, as these diseases cause predictable changes in the protein pattern.
Identifying the Five Major Protein Fractions
The electrophoresis process resolves serum proteins into five main groups, or fractions. The first and largest peak is Albumin, constituting about 60% of the total serum protein in a healthy individual. Albumin’s main biological roles include maintaining fluid balance (osmotic pressure) and transporting substances like hormones, fatty acids, and certain medications throughout the bloodstream.
Following albumin are the globulin fractions:
- Alpha-1 globulins: Includes proteins like alpha-1 antitrypsin, an enzyme inhibitor.
- Alpha-2 globulins: Contains larger proteins such as haptoglobin and alpha-2 macroglobulin.
- Beta globulins: Composed of transferrin, which transports iron, and beta-lipoproteins, which carry cholesterol.
- Gamma globulins: The final and most heterogeneous group, primarily consisting of antibodies (immunoglobulins).
These immunoglobulins are produced by plasma cells and are responsible for the body’s long-term immune defense. In a normal pattern, this fraction appears as a broad, diffuse band, reflecting the diverse range of antibodies needed to fight various pathogens.
Linking Abnormal Patterns to Disease
Diagnostic interpretation relies on identifying specific changes in the size and shape of the five protein peaks. A characteristic finding in plasma cell malignancies, such as multiple myeloma, is the “Monoclonal Spike.” This appears as a single, narrow, densely stained peak, usually in the gamma region, representing the overproduction of a single, identical type of immunoglobulin by abnormal plasma cells.
An “Acute Phase Reaction,” seen during infection or inflammation, is marked by an increase in the Alpha-1 and Alpha-2 fractions, as these proteins participate in the early immune response. Conversely, Nephrotic Syndrome (a kidney disorder) causes a decrease in albumin due to its loss in the urine, often accompanied by an increase in the larger Alpha-2 globulins that the damaged kidneys retain. Chronic liver disease, such as cirrhosis, results in a “polyclonal gammopathy”—a broad, dome-shaped elevation in the entire gamma region—reflecting the immune system’s generalized response to chronic inflammation. These distinct shifts in the protein profile provide valuable clues that guide further testing and help establish a diagnosis.