Analysis of cell surface light chain immunoglobulin expression by flow cytometry in normal controls: a new mathematical approach.

: It has been observed in flow cytometric studies that in normal individuals there are proportionally more kappa+ than lambda+ bearing light chain B-cells. Overt predominance of one type of light chain bearing cell over the other is a characteristic of B-cell neoplasias, a phenomenon called clonal excess (CE). A mathematical model using the Weibull distribution is proposed for studying such an excess. The new approach is desirable for two reasons: First, it is parametric and hence offers a more sensitive and versatile analysis than its nonparametric counterparts. Second, it utilizes only the relevant information from the upper tails of the distributions of the fluorescence intensity of the kappa+ and lambda+ cells. Two measures of CE based on the Weibull model are proposed, and a normal range of variability was determined for each measure using a random sample of 48 normal controls. Such normal ranges are particularly useful in detecting cancer patients with minimal B-cell neoplasias. A comparative study of the new measures, Ault's maximum difference measure, and a measure based on Ligler's method showed that the parametric approach provides much more sensitivity than both the nonparametric ones.