The effect of reduction of IgM on the quantitative determination of IgM by radial immunodiffusion and turbidimetry.

The behaviour of different IgM proteins in radial immunodiffusion was investigated. In agreement with earlier findings differences were observed between various IgM preparations, which disappeared after reduction of IgM. The amount of IgM in several standard sera, that are used for the quantitative determination of IgM, was measured by radial immunodiffusion after reduction of IgM, and was found to be lower than hitherto accepted. It was observed that it was not necessary to perform reduction of IgM before its quantitation when a turbidimetric immunoassay was used. We conclude that (1) the standard sera that are used for the determination of IgM have to be calibrated in radial immunodiffusion after reduction of IgM and (2) the absolute amount of IgM in sera is about 0.6 times the amount that is commonly accepted.