Serum Protein Electrophoresis (SPEP) Test

Test Overview

The serum protein electrophoresis (SPEP) test measures specific proteins in the blood to help identify some diseases. Proteins are substances made up of smaller building blocks called amino acids. Proteins carry a positive or a negative electrical charge, and they move in fluid when placed in an electrical field. Serum protein electrophoresis uses an electrical field to separate the proteins in the blood serum into groups of similar size, shape, and charge.

Blood serum contains two major protein groups: albumin and globulin. Both albumin and globulin carry substances through the bloodstream. Using protein electrophoresis, these two groups can be separated into five smaller groups (fractions):

• Albumin. Albumin proteins keep the blood from leaking out of blood vessels. Albumin also helps carry some medicines and other substances through the blood and is important for tissue growth and healing. More than half of the protein in blood serum is albumin.
• Alpha-1 globulin. High-density lipoprotein (HDL), the "good" type of cholesterol, is included in this fraction.
• Alpha-2 globulin. A protein called haptoglobin, which binds with hemoglobin, is included in the alpha-2 globulin fraction.
• Beta globulin. Beta globulin proteins help carry substances, such as iron, through the bloodstream and help fight infection.
• Gamma globulin. These proteins are also called antibodies. They help prevent and fight infection. Gamma globulins bind to foreign substances, such as bacteria or viruses, causing them to be destroyed by the immune system.

Each of these five protein groups moves at a different rate in an electrical field and together form a specific pattern. This pattern helps identify some diseases.