Method-specific variations in the calibration of a new immunoglobulin standard suitable for use in nephelometric...

The putative International Federation of Clinical Chemistry immunoglobulin standard, IFCC 74/1, was calibrated against the World Health Organization (WHO) immunoglobulin standard 67/99 by three different methods: automated immunoprecipitation, Laurell rocket immunoelectrophoresis, and radial immunodiffusion. The same antisera were used in all the assays, which were performed in five expert laboratories. With the aid of linearizing transformations for the dilution curves of both materials and use of a carefully weighted statistical evaluation, values in International Units for IgG, IgA, and IgM were ascribed to IFCC 74/1. The values achieved by the three different methods were not statistically different, except in the case of IgA. IgM assays by automated immunoprecipitation were excluded owing to a high degree of imprecision.