immunofixation

Immunofixation electrophoresis (IFE) is a laboratory technique used to identify and type monoclonal immunoglobulins in serum or urine. It is routinely employed in the workup of suspected monoclonal gammopathies such as multiple myeloma, Waldenström macroglobulinemia, and other conditions that produce a single clone of immunoglobulin or light chains.

The method combines electrophoresis and immunoprecipitation. Proteins in a specimen are first separated by electrophoresis on a support medium. After separation, antisera specific for immunoglobulin heavy chains (IgG, IgA, IgM) and light chains (kappa, lambda) are applied in separate lanes. Antibody binding to a monoclonal protein forms discrete precipitin bands at the position corresponding to the monoclonal protein, allowing determination of the class and light-chain type. The pattern is interpreted as monoclonal when a single, discrete band is present (often with corresponding heavy-chain and light-chain specificity), and polyclonal when multiple diffuse bands appear.

IFE is more sensitive than standard serum protein electrophoresis for detecting small amounts of monoclonal protein and is also used to characterize and monitor M-proteins during treatment. It is commonly performed after initial SPEP and can be applied to urine to detect Bence Jones proteins, providing valuable diagnostic and monitoring information.

Limitations include semi-quantitative results, dependence on antibody reagents and technical execution, and potential ambiguity in complex immune profiles. Quantitative assessment of monoclonal protein typically relies on other assays; immunofixation complements these tests for precise typing and clonality.