Critical evaluation of the serum kappa/lambda light-chain ratio in the detection of M proteins

Restricted immune responses may become manifest as humoral immune deticiency, as paraproteinemia caused by an overstimulated clone of B ceils, or as an underlying B-cell malignancy. M proteins are recommended to be identified by electrophoresis and characterised by immunoelectrophoresis or preferably immunofixation [ 1,2]. However, these methods call for considerable expertise and are timeconsuming. It is essential to discover and characterise M proteins and distinguish benign paraproteins from malignant ones. The recent development of assays for kappa and lambda light chains has led to the proposal that a disturbance of the kappato-lambda ratio might be used to detect, characterise and confirm M-componentrelated immunoglobulin abnormalities [3-51. Measurement of immunoglobulin light chains involves less work and time than electrophoresis or immunotixation, but the clinical utility and diagnostic sensitivity of light-chain dete~inations have been questioned [6]. We have recently shown that nephefometric determination of M proteins is rapid, precise and reliable, without the risk of antigen excess [7]. This prompted us to examine population-based reference values for light chains and compare the performance nephelometric characterisation of M-protein light chains with results obtained by conventional cellulose acetate electrophoresis and immunotixation.