Immunoquantitation of free light chain immunoglobulins: applications in multiple myeloma.

A single radial immunodiffusion (RID) assay for the free lambda (lambda) and kappa (kappa) light chain (LC) immunoglobulins was developed for study of clinical samples of serum, urine, and bone marrow of patients with multiple myeloma. Using highly specific rabbit anti-LC sera, we were able to quantitate: (a) free serum LC after fractionating the serum sample using an Amicon ultrafiltration chamber equipped with an XM100A diaflow membrane and an 125I-LC standard for calculating filtration efficiencies, (b) directly, Bence Jones (BJ) proteins in the urine, and (c) the in vitro LC synthesis by myeloma plasma cells obtained from bone marrow aspirates. The median values of free LC levels in sera (n = 12), urines (n = 25), and marrow culture synthetic rates (n = 17) were 116.2 mg/dl, 0.775 g/day and 15.3 pg/plasma cell/day, respectively. These data were useful in initial evaluation of patients and serial follow-up studies. The assays have also been of use in our research on the determination of total body tumor mass in patients with BJ multiple myeloma.