Serum globulin electrophoresis
Alternative names:
globulin electrophoresis (SPEP)
How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
Electrophoresis is a laboratory technique. The blood serum (the fluid portion of blood) is placed on specially treated paper and exposed to an electric current. The various proteins migrate (move on the paper) to form bands that indicate the relative proportion of each protein fraction.
How to prepare for the test:
Fast for 4 hours before the test. The health care provider may advise you to withhold drugs that can interfere with the test (see special considerations).
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel:
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed:
This test is performed when the amount of globulin proteins are of particular interest. Identification of the various types of globulins (globulin electrophoresis) can be useful in the diagnosis of various disorders (see "What do abnormal results mean").
Proteins are important constituents of all cells and tissues. Proteins are made from amino acids. There are many different kinds of proteins in the body with many different functions, for example, enzymes, some hormones, hemoglobin (oxygen transport), LDL (cholesterol transport), fibrinogen (blood clotting), collagen (structure of bone and cartilage), and immunoglobulins (antibodies).
Serum proteins are grossly separated into albumin and globulins, that is, total protein = albumin + globulin. Albumin is the protein of highest concentration in the serum (plasma, the fluid portion of blood, is serum plus fibrinogen). Albumin is a carrier of many small molecules, but is also of prime importance in maintaining the oncotic pressure of the blood (that is, keeping the fluid from leaking out into the tissues).
Globulins are roughly divided into alpha, beta, and gamma globulins. These can be separated and quantitated in the laboratory by electrophoresis and densitometry. The gamma fraction includes the various types of antibodies (immunoglobulins M, G, and A).
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