What is an immunofixation test?

Updated: Jul 29, 2019
  • Author: Anastasios Dimou, MD; Chief Editor: Eric B Staros, MD  more...
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Immunofixation consists of an electrophoresis phase and a fixation phase. [1] In the former, the serum is applied to an agarose gel, and the negatively charged serum proteins move toward the cathode under the influence of an electric current. The speed of movement is dictated by their charge. During the fixation phase, antiserum containing anti-IgG, anti-IgA, anti-IgM, anti-light chain kappa, or anti-light chain lambda is inoculated with the serum proteins. If a monoclonal protein is present, a precipitant will form at this phase. Finally, the sample is washed to remove the proteins that do not precipitate and then stained, destained, and dried.

In most cases in which a monoclonal protein is present, it shows as a narrow band at the IgG lane in combination with a monoclonal band at the kappa or lambda lane. IgA or IgM bands are less common. Finally, isolated light chain bands, either kappa or lambda, represent more commonly pure kappa or lambda light chain gammopathies or, less commonly, immunoglobulin D (IgD) or immunoglobulin E (IgE) gammopathies. Given the dismal impact on prognosis in the latter scenario, [12] an additional assay for the identification of IgD or IgE must be performed. If the result is negative, it is safe to conclude that a pure kappa or lambda light chain is present. [10]

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