Desirable performance characteristics and clinical utility of immunoglobulin and light-chain assays derived from data on biological variation.

Using automated assays of IgG, IgA, and IgM, and kappa (kappa) and lambda (lambda) light-chains, we assessed the analytical, intra-individual, and interindividual components of variation in a cohort of 12 apparently healthy subjects to examine the utility of the Kallestad Immunochemical Evaluation system. The immunoglobulins and light-chains had small intra-individual variation, and, in consequence, good analytical precisions (CV) of 2.3%, 2.5%, 3.0%, 2.4%, and 2.4% are required for IgG, IgA, IgM, kappa, and lambda assays, respectively. All of these analytes, and the derived kappa/lambda and heavy-/light-chain ratios, have marked individuality. Conventional population-based reference values are of limited utility; therefore, the assays are unlikely to have high diagnostic sensitivity but will be very useful for monitoring individuals. The kappa/lambda ratio may be of particular value in monitoring because a change exceeding 4% does imply a significant (P less than or equal to 0.05) difference in serial results.