Medical and technical usefulness of measurement of kappa and lambda immunoglobulin light chains in serum with an M-component.

Kappa and lambda-immunoglobulin light chains were measured to evaluate their usefulness for identifying monoclonal components in serum. Reference concentrations of the Ig light chains were evaluated by the analysis of the serum of 50 blood donors. Two hundred and fifty patients were selected for the presence of an M-component in their serum, which was detected by serum electrophoresis on agarose. The heavy and light chains of the M-component were identified by immunofixation. The concentrations of the three major immunoglobulin classes and of the two light chain types were measured by immunonephelometry. On the basis of the Ig kappa/lambda ratio alone, the Ig light chain type was correctly identified in 76% of the M-components, and there were no misidentifications. By comparing the calculated concentrations of M-component and residual polyclonal Ig with the measured concentrations of the 3 major Ig classes, it was possible to identify the heavy chain type of 58% of the M-components. These observations suggest that M-components can often be identified by the measurement of Ig light chains, a procedure involving less work and time than immunofixation. Moreover, the follow up of gammapathies could benefit from quantitative parameters evaluated from the Ig light chain concentrations: the concentration of the M-component, the ratio of M-component vs total Ig of the same class, and the ratio of M-component vs the sum of the 3 major Ig classes.