Differentiation of benign monoclonal gammopathy and smouldering multiple myeloma from frank myeloma.

Circulating immunoglobulin (Ig) secreting cells of each type of the different Ig classes were enumerated using a reverse haemolytic plaque assay in nine subjects with the pre-clinical phase of IgG myeloma (six with benign monoclonal gammopathy and three with smouldering multiple myeloma). A shift in the ratio of IgG kappa to IgG lambda secreting cells without a significant increase in the total number of IgG secreting cells, that is the number of IgG kappa plus IgG lambda secreting cells, was a constant feature noted in every subject.