Accurate Quantification of Monoclonal Immunoglobulins Migrating in the Beta Region on Protein Electrophoresis.

Background: The concentration of monoclonal immunoglobulins (Igs) in neoplastic monoclonal gammopathic manifestations is generally measured by densitometric scanning of the monoclonal peaks on gel or by measuring absorbance at 210 nm in capillary electrophoresis (CE). For monoclonal Igs migrating in the beta region, measurement is complicated by the major beta-region proteins, namely, transferrin and C3.

Methods: C3 interference in densitometry was eliminated by heat treatment of serum, and monoclonal Igs were quantified by densitometry of the residual band. The immunochemical measurement of transferrin was converted to its equivalent densitometric quantity. For monoclonal Ig migrating with transferrin, the contribution of the latter was removed by subtracting the converted transferrin concentration from the combined densitometric quantification of the band. With CE, monoclonal Ig was measured by using immunosubtraction (ISUB) to guide demarcation.

Results: The results obtained using the C3 depletion and transferrin subtraction method were lower and yet comparable to the results derived from using CE measurement guided by ISUB. As we expected, the results from both methods were lower than those derived from a perpendicular drop measurement of the peak or via nephelometric assay of the involved isotype.

Discussion: Accurate measurement of monoclonal Igs is important for the diagnosis and monitoring of monoclonal gammopathic manifestations. Determination of serum free light chain concentration per gram of monoclonal Ig is an essential measure for the diagnosis of light chain-predominant multiple myeloma. The method described herein improves accuracy of measurements for monoclonal Igs migrating in the beta region, without the need for special reagents or equipment.