Serum protein electrophoresis (SPEP or SPE) is a laboratory test that examines specific proteins in the blood called globulins. The most common indications for a serum protein electrophoresis test are to diagnose or monitor multiple myeloma, a monoclonal gammopathy of uncertain significance (MGUS), or further investigate a discrepancy between a low albumin and a relatively high total protein. Unexplained bone pain, anemia, proteinuria, chronic kidney disease, and hypercalcemia are also signs of multiple myeloma, and indications for SPE. Blood must first be collected, usually into an airtight vial or syringe. Electrophoresis is a laboratory technique in which the blood serum (the fluid portion of the blood after the blood has clotted) is applied to either an acetate membrane soaked in a liquid buffer, or to a buffered agarose gel matrix, or into liquid in a capillary tube, and exposed to an electric current to separate the serum protein components into five major fractions by size and electrical charge: serum albumin, alpha-1 globulins, alpha-2 globulins, beta 1 and 2 globulins, and gamma globulins.
Acetate or gel electrophoresis
Proteins are separated by both electrical forces and electroendoosmostic forces. The net charge on a protein is based on the sum charge of its amino acids, and the pH of the buffer. Proteins are applied to a solid matrix such as an agarose gel, or a cellulose acetate membrane in a liquid buffer, and electric current is applied. Proteins with a negative charge will migrate towards the positively charged anode. Albumin has the most negative charge, and will migrate furthest towards the anode. Endoosmotic flow is the movement of liquid towards the cathode, which causes proteins with a weaker charge to move backwards from the application site. Gamma proteins are primarily separated by endoosmotic forces. The drawing of the electrophoretic bands provided by the laboratory may be difficult to remember, and medical students, residents, nurses, and non-specialized medical practitioners may find visual mnemonics useful to recall the five main bands and the shape of normal serum electrophoresis.
Capillary electrophoresis
In capillary electrophoresis, there is no solid matrix. Proteins are separated primarily by strong electroendosmotic forces. The sample is injected into a capillary with a negative surface charge. A high current is applied, and negatively charged proteins such as albumin try to move towards the anode. Liquid buffer flows towards the cathode, and drags proteins with a weaker charge.
Serum protein fractions
Albumin
Albumin is the major fraction in a normal SPEP. A fall of 30% is necessary before the decrease shows on electrophoresis. Usually a single band is seen. Heterozygous individuals may produce bisalbuminemia – two equally staining bands, the product of two genes. Some variants give rise to a wide band or two bands of unequal intensity but none of these variants is associated with disease. Increased anodic mobility results from the binding of bilirubin, nonesterified fatty acids, penicillin and acetylsalicylic acid, and occasionally from tryptic digestion in acute pancreatitis.
Absence of albumin, known as analbuminaemia, is rare. A decreased level of albumin, however, is common in many diseases, including liver disease, malnutrition, malabsorption, protein-losing nephropathy and enteropathy.
Albumin – alpha-1 interzone
Even staining in this zone is due to alpha-1 lipoprotein (high density lipoprotein – HDL). Decrease occurs in severe inflammation, acute hepatitis, and cirrhosis. Also, nephrotic syndrome can lead to decrease in albumin level; due to its loss in the urine through a damaged leaky glomerulus. An increase appears in severe alcoholics and in women during pregnancy and in puberty.
The high levels of AFP that may occur in hepatocellular carcinoma may result in a sharp band between the albumin and the alpha-1 zone.