A modification of the automated immune precipitin method for quantitation of human serum immunoglobulins

Challenges of measuring monoclonal proteins in serum

The measurement of monoclonal protein (M-protein) is vital for stratifying risk and following individuals with a variety of monoclonal gammopathies. Direct measurement of the M-protein spike by electrophoresis and immunochemical measurements of specific isotypes or free light chains pairs has provided useful information about the quantity of M-protein. Nonetheless, both traditional electrophoresis and immunochemical methods give poor quantification with M-proteins smaller than 10 g/L (1 g/dL) when in the presence of polyclonal immunoglobulins that co-migrate with the M-protein. In addition, measurements by electrophoresis of M-proteins migrating in the β- and α-regions are contaminated by normal serum proteins in those regions. The most precise electrophoretic method to date for quantification involves exclusion of the polyclonal immunoglobulins by using the tangent skimming method on electropherograms, which provides a 10-fold improvement in precision. So far, however, tangent measurements are limited to γ migrating M-proteins. Another way to improve M-protein measurements is the use of capillary electrophoresis (CE). With CE, one can employ immunosubtraction to select a region of interest in the β region thereby excluding much of the normal proteins from the M-protein measurement. Recent development of an immunochemical method distinguishing heavy/light chain pairs (separately measuring IgGK and IgGL, IgAK and IgAL, and IgMK and IgML) provides measurements that could exclude polyclonal contaminants of the same heavy chain with the uninvolved light chain type. Yet, even heavy/light results contain an immeasurable quantity of polyclonal heavy/light chains of the involved isotype. Finally, use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) looms on the horizon as a means to provide more consistent and sensitive measurements of M-proteins.

Multiple myeloma: current concepts in diagnosis and management

The basic pathologic process in multiple myeloma is the neoplastic proliferation of a single clone of plasma cells. Although the events which trigger autonomous cell growth are not well understood, the secretion of an M component, a serum or urinary immunoglobulin molecule or a light chain fragment by the vast majority of myeloma cells has provided a biologic marker which has greatly facilitated the study of this disease Some of the more recent clinical concepts which have evolved from studies on the plasma cell and the immunoglobulin molecule are discussed.

Comparison of nephelometry and immunofluorescence for immunoglobulin quantitation in pathologic sera

Nephelometers from Beckman, Hyland and Technicon, and the immunofluorescent system from International Diagnostic Technology were evaluated for IgG, IgM, and IgA quantitation in pathologic sera. Within-run, between-run, and between-day imprecision of each instrument varied for each immunoglobulin and for different levels of the same immunoglobulin. Thus, no instrument showed clearly superior precision. However, for elevated immunoglobulin levels, Technicon had poorer between-day precision than the other instruments (p less than 0.05). Comparison of monoclonal immunoglobulin quantitation with monoclonal protein quantitation by serum protein electrophoresis in 13 patients showed best correlation for the Beckman instrument (r = 0.942). Quantitation of IgG, IgM, and IgA in 50 specimens required approximately 330, 390, 480, and 480 min to complete with Hyland, International Diagnostic Technology, Beckman, and Technicon, respectively. Our evaluation suggests that the proportion of abnormal specimens in the workload and the availability of reagents for desired assays should be considered in determining the suitability of one of these instruments for a particular laboratory.