Serum beta-2-microglobulin binding activity in monoclonal gammopathy: correlative study and clinical significance.

Serum beta 2m binding activity (S beta 2m-BA) was determined by a polyethylene glycol exclusion test of radiolabeled human beta 2m in 185 serum samples from 62 patients with multiple myeloma (MM). Elevated S beta 2m-BA was found in more than half of the samples from IgG myeloma taken before treatment or during progression of the disease but not during the plateau-phase. Conversely, elevated S beta 2m-BA was found in only one case of IgA myeloma, one case of monoclonal gammopathy of undetermined significance and none of the Bence Jones myelomas. S beta 2m-BA appears to be related to disease progression in IgG myeloma. The activity is supported by minute amounts of serum autoantibodies which are distinct from the monoclonal component. S beta 2m-BA was independent from serum beta 2m levels.