Serum protein electrophoresis

Kristiina Ruotsalo, DVM, DVSc, ACVP & Margo S. Tant, BSc, DVM, DVSc
Original article: Serum Protein Electrophoresis - General

What are serum proteins?

Serum is the liquid part of the blood from which red blood cells, white blood cells and blood clotting factors have been removed. The serum contains a large amount of protein, which performs various functions. These functions include providing cell nutrition, protecting against infections, acting in inflammation, and acting as hormones or enzymes.

What is serum protein electrophoresis?

Protein electrophoresis is a specialized test that analyzes specific groups of proteins in the blood serum and measures the proportion of each group of proteins. Individual proteins have characteristic sizes and electric charges. Electrophoresis divides serum proteins into broad groups based on their size and electrical charge. The results of the analysis are shown in a special graph and a pattern of different proteins is used to diagnose specific diseases, including some types of cancer.

What proteins does the test measure?

"Globulin levels - tend to rise in diseases."

There are many different proteins in the blood, but protein electrophoresis focuses on only two classes of proteins, called albumin and globulin. There is only one type of albumin and it is found in the blood at relatively constant levels; it is a versatile protein with a number of important roles, including the transport of substances in the body. In contrast, there are many types of globulins, each with a specific function. Globulin levels are more variable than albumin and tend to increase in disease.

When a blood sample is analyzed by routine methods, albumin and total globulin levels are measured. Protein electrophoresis goes further and divides the total globulin into its individual parts, called globulin fractions, which are then measured individually. By analyzing the types and amounts of different proteins in your blood, it is often possible to determine the nature of your pet's disease.

Typically, globulins are divided into the following fractions: α1 (Alpha 1), α2 (Alpha 2), β1 (Beta 1), β2 (Beta 2), γ (Gamma)

Why are globulins important?

Globulins play an important role in the body's defense system; some are "first rescuers," like firefighters, and quickly appear in the bloodstream after any tissue injury. Others, called antibodies, are produced by lymphoid cells, a type of white blood cell, and appear in the bloodstream more slowly after injury. Antibodies are essential for the body's ability to defend itself against bacteria and other disease-causing organisms.

High total blood globulin levels in most cases indicate underlying inflammation or infectious disease, but sometimes indicate the presence of cancer, especially affecting lymphoid cells. When determining the type and distribution of globulins, protein electrophoresis can help us decide what kind of disease it may be.

How does the test work?

Belch electrophoresis is like sorting a bowl of mixed colored beads into separate groups according to color and size and then counting how many beads are in each group. The test is based on the fact that albumin and different globulins have different sizes and that each type of protein carries a different electrical charge than static electricity. The serum sample is prepared and placed on a special grid. When an electric current is applied, different proteins migrate across the lattice at different rates, causing them to divide into groups according to size and electric charge. For example, albumin is a relatively small molecule and carries a lot of "static electricity"; it travels the farthest and fastest of all proteins and is always the first to appear on the chart. Globulins are generally larger and move more slowly, and antibodies, which are the largest of globulins and have the least "static electricity", move very slowly and are the last to be shown on the graph.

"… Each type of protein carries a different electric charge"

Once the proteins are divided into their groups, it is possible to measure the amount of each protein and display the results in a graph. The shape of the graph helps us to understand the underlying disease.

When should protein electrophoresis be done?

"Protein electrophoresis is recommended whenever total globulin levels are elevated and the cause is unknown."

Protein electrophoresis is recommended whenever total globulin levels are elevated and the cause is unknown. The higher the level of total globulins, the more suitable it is to perform protein electrophoresis. Globulins usually grow when there is inflammation, tissue injury or infectious disease. More importantly, however, globulin levels can be very high in some types of lymphoid cell cancers. When preliminary blood tests indicate that total globulin levels are elevated, protein electrophoresis should be performed to try to determine if the underlying disease is inflammatory or neoplastic.

How is the graph (electrophoretogram) interpreted?

The most important thing in interpreting the electrophoresis graph is whether the globulin is increased due to the growth of many different globulins or due to the growth of only one type of globulin. When many different globulins are elevated, we speak of a polyclonal increase (poly = many; clonal = type); when only one type of globulin is responsible for the increase, we speak of a monoclonal increase (mono = one; clonal = type). Inflammation is typically polyclonal, while lymphoid neoplasia is more likely to be monoclonal. Unfortunately, there is some overlap between the two general classifications.

Do the results always provide a definitive diagnosis?

No, but some serious diseases, both inflammatory and neoplastic, form a characteristic pattern on the electrophoresis chart that can quickly lead to a definitive diagnosis. In many inflammatory conditions, protein electrophoresis can provide valuable information about the severity of inflammation, where it may be located, and what it may cause.

Examples of electrophoretogram

Panel A: Normal agarose gel electrophoretogram in dogs. The highest peak on the left is albumin, followed by α1 (2 peaks), α2 (2 peaks), β1 (2 peaks, β1a and β1b), β2 and γ (last flat peak).
Panel B: Serum from a cat with a virus infection feline infectious peritonitis (FIPV). Visible increase α2 globulins (arrow), indicating acute phase reactant response, and polyclonal gammopathy (arrow in the γ region). These results are typical, but not specific, for FIPV infection (they can be observed in other inflammatory conditions).
Panel C: Serum from a dog with multiple myeloma. There is a high narrow peak in the γ region, which indicates monoclonal gammopathy (arrow). Albumin concentrations are also reduced (compared to a normal dog in panel A).

Co-authors: Kristiina Ruotsalo, DVM, DVSc, ACVP & Margo S. Tant, BSc, DVM, DVSc

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