Two nephelometric methods compared with a radial immunodiffusion method for the measurement of IgG, IgA and IgM.

1. The IgG, IgA and IgM concentrations of a group of 100 or more human sera found by both the rate nephelometric Beckman Immunochemistry System and the endpoint Behring Laser Nephelometer procedure gave good correlations when compared to results obtained by an endpoint radial immunodiffusion method. The correlation coefficients for the Behring method comparisons were 0.958 for IgG, 0.979 for IgA and 0.966 for IgM when only values under 850 IU of IgM/ml were considered. The Beckman system gave correlation coefficients of 0.984 for IgG, 0.993 for IgA and 0.986 for IgM when IgM concentrations were under 500 IU/ml. Determinations from all three methods agreed well except for very high IgM values which were considerably higher by RID. 2. Both nephelometric methods are fast and precise. The average within-run coefficients of variation were 2.6% for the Behring method, 2.2% for the Beckman system and 2.1% for radial immunodiffusion while average between-run precision values of 6.9% for the Behring method, 3.7% for the Beckman system and 4.9% for radial immunodiffusion were found. The Beckman rate system has the advantage of one point calibration, ease of data processing and elimination of sample blanks.