Laboratory tests used to measure paraprotein
The main tests used to detect paraprotein and free light chains in the blood and urine are described below. As well as being important in confirming a diagnosis of myeloma, they are also very useful in helping to track the activity of the myeloma and the response to treatment.
Serum protein electrophoresis
Serum protein electrophoresis (SPEP) is a laboratory test that separates proteins in a blood sample, based on their size or other physical characteristics.
A patient’s blood serum sample is placed on a special paper treated with gel which is exposed to an electrical current. This separates the serum proteins according to size and charge into a characteristic banded pattern. The thickness of each band represents the amount of a specific protein. In myeloma, paraprotein appears as a single heavy band in what is known as the gamma fraction and can be depicted on a graph as a single tall spike (Figure 1).
Urine protein electrophoresis
Urine protein electrophoresis (UPEP) is performed in the same way as SPEP and is used to measure urinary Bence Jones (free light chain) protein. Sometimes, the urine sample may need to be concentrated and importantly, the urine sample should be kept refrigerated to prevent the proteins from breaking down.
Bence Jones protein appears in the gamma fraction and the profile generated is similar to SPEP except that the albumin peak is much lower.
Immunofixation electrophoresis
Immunofixation (IFE) is the most sensitive type of electrophoresis. It is used to provide more specific information about the paraprotein. After proteins have been separated by standard electrophoresis, antiserum against lgG, IgA, 1gM, lgD, IgE, κ and λ light chains are applied to the electrophoresis gel. A complex forms between the protein and corresponding antiserum that can then be stained to identify involved Ig and light chain.
IFE is useful to assess changes and proportions of various proteins. It is a very sensitive technique and can detect small amounts of paraprotein even when SPEP and UPE are negative. Paraprotein can be detected in the serum or urine from 99% of myeloma patients with IFE and is the main method for classifying the type of myeloma a patient has e.g. IgA kappa.
Immunoelectrophoresis
Immunoelectrophoresis (IEP) employs a technique similar to IFE, but includes a sample of the patient’s serum or urine together with antisera against lgG, IgA, 1gM, lgD, IgE, κ and λ light chains in the electrophoresis gel. At the site where the patient’s paraprotein meets the corresponding antiserum, an arc of precipitation forms.
This test is used to detect paraprotein and to type it. As with IFE, IEP is also much more sensitive than SPEP and UPEP and can detect small amounts of paraprotein even when SPEP and UPEP are negative. However, IFE is generally preferred as it is technically easier and more reliable.