Six approaches to routine quantification of human monoclonal immunoglobulin M compared

Six routine techniques for the determination of monoclonal IgM are compared: standard electrophoresis, the Technicon AIP system, Hyland laser nephelometry, Beckman Immunochemistry System, Behring laser nephelometry, and radial immunodiffusion. The data are evaluated by use of a nonparametric statistical analysis of variance by ranks (Friedman test) and Wilcoxon's test. The 27 sera containing monoclonal IgM that we studied yielded different results by the various techniques. Sera from a "reference" population of 15 subjects having above-normal polyclonal IgM yielded identical results for all techniques. These statistical findings agree with the biophysical mechanisms involved in the various ways of quantifying IgM. We conclude that these different systems are equivalent for estimating polyclonal IgM, but cannot (and should not) yield identical values when used in monoclonal IgM evaluations. Results for monoclonal IgM must be interpreted in terms of the molecular forms and immunological specificities of the assayed IgM.