Limitations of numerical ratios for defining monoclonality of immunoglobulin light chains in B-cell lymphomas

Hematopathologists sometimes rely upon the "monoclonality" of immunoglobulin light chains of B-cells as an indicator of malignancy in lymph node biopsies. The validity of using the ratio of kappa to lambda light chains for defining monoclonality has not been statistically established, however. We examined with flow cytometry 57 unequivocal B-cell lymphomas and 49 benign lymphoid hyperplasias. Our purpose was to define and study the optimal numerical criteria for discriminating between B-cell lymphomas and benign hyperplasia on the basis of the kappa:lambda ratio. The data indicate that ratios less than .7 or greater than 5.5 are the optimum for discriminating between lymphoma and benign hyperplasia, but they have a false negative rate of approximately 27% and a 6% false positive rate. The reasons for the relatively low sensitivity are discussed. We conclude that kappa:lambda ratios are a fairly specific but insensitive parameter for distinguishing between B-cell lymphoma and benign lymphoid hyperplasia.