Clinical significance of 7s IgM in monoclonal IgM diseases.

The sera from 117 patients with diseases associated with a high production of monoclonal IgM were analysed for the presence of low molecular weight (7s) IgM by using a simple thin-layer Sephadex technique. 7s IgM was found in the sera of patients with myelomata (66%), lymphomata (45%), and Waldenström's macroglobulinaemia (20%), but was absent from the sera of patients with benign monoclonal macroglobulinaemia.This technique provides a cheap and practical test which may be valuable in selecting patients with lymphomata from those with benign lesions.