Surface immunoglobulin light chain restriction in B-cell non-Hodgkin's malignant lymphomas

Twenty-four control cases of reactive follicular hyperplasia (RFH) and 28 cases of B-cell non-Hodgkin's malignant lymphoma (ML) were evaluated for surface immunoglobulin (sIg) light chain expression with flow cytometry. Because there was no significant difference between the distribution of the ML κ/λ ratios for which κ/λ >1 compared with those ML λ/κ ratios for which λ/κ >1 using the Kolmogorov-Smirnov statistic, the authors treated κ/λ data symetrically. By transforming all κ/λ ratios to maximum ratios, that is, R(max) = max (κ/λ, λ/κ), so that all resulting ratios wer at least one, the authors defined a new statistic for evaluating sIg light chain restriction. There was a highly significant difference for equality of distribution of the data using the Mann-Whitney test (P < 0.0001). By choosing cut-points based on the R(max) statistic, the authors were able to separate the RFH and ML cases with sensitivity = 0.96 ± 0.07 (95% confidence) and with specificity = 0.91 ± 0.11 (95% confidence). These point estimates of sensitivity and specificity appear to be promising for the clinical utility of the R(max) statistic, even for cases of B-cell ML with discordantly low expression of sIg light chains. The R(max) statistic will facilitate the comparison of data between different laboratories because it does not require assignment of cut-points and can be made using a simple nonparametric test.