Immunochemical Characterization of Immunoglobulins in Serum, Urine, and Cerebrospinal Fluid

The characterization of immunoglobulins spans a spectrum of methods, including molecular analysis of gene usage and rearrangement, quantitation of immunoglobulin heavy chains as well as intact and free light chains, qualitative assessment and characterization of clonality, and identification of abnormalities that may be clinically significant, such as hyperviscosity syndrome, cryoglobulinemia, and amyloidosis (AL). This chapter focuses on qualitative methods for the assessment and characterization of clonality. The methods include agarose gel electrophoresis (AGE) with immunofixation, capillary electrophoresis (CE) with immunosubtraction (ISUB), and isoelectric focusing with immunoblotting or immunofixation. All three methods can be used to identify monoclonal, oligoclonal, and polyclonal immunoglobulin populations and to identify the heavy and/or light chains contained in the population. Immunofixation electrophoresis (IFE) and ISUB electrophoresis are diagnostic tools used for the identification of monoclonal gammopathies and, conversely, for the confirmation of polyclonal hypergammaglobulinemia. Isoelectric focusing with immunoblotting or immunofixation is a cerebrospinal fluid (CSF) diagnostic test for the identification of oligoclonal bands in multiple sclerosis (MS).