Diagnostic value of the concentration of M-component in initial classification of monoclonal gammopathy.

The diagnostic value of the concentration of a serum M-component in initial classification of monoclonal gammopathy into malignant monoclonal gammopathy (MMG) and monoclonal gammopathy of undetermined significance (MGUS) was evaluated in 315 consecutive individuals with IgG, IgA or IgM type M-components. The final diagnosis was MMG in 84 and MGUS in 231 patients. Serum concentration was significantly highest in MMG, but for all 3 kinds of M-components, overlapping serum concentrations between MMG and MGUS were found. Highest efficiency was reached with a serum concentration of 30.2 g/l for IgG, 26.6 g/l for IgA and 22.7 g/l for IgM. Using these values, an initial correct classification was achieved in 0.90 of IgG M-components, in 0.91 of IgA M-components and in 0.79 of IgM M-components. Normal levels of uninvolved immunoglobulins were found to point strongly to MGUS.