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 < 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.