Studies of Bence Jones Proteins by Immunonephelometry*t

Plasma cell dyscrasia is a disease caused by a monoclonal population of plasma cells. Most often the workup for this disease is prom pted by the appearance of a paraprotein in serum, but a significant num ber of cases exhibit only a Bence Jones protein. Immunofixation electrophoresis is the most sensitive m ethod presently used for identifying Bence Jones protein­ uria. This methodology is laborious, expensive, and difficult to interpret. As a result, quantitative immunochemical methodologies have been sug­ gested for m easuring Bence Jones proteinuria. In this m anuscript, it is demonstrated by rate nephelom etry that: (1) although serum polyclonal immunoglobulins are accurately m easured as compared to the calibration material, serum monoclonal immunoglobulins are not; (2) m easurem ent of immunoglobulins in the urine of patients with generalized proteinuria is biased towards an increased num ber of light chains or a decreased num ber of heavy chains; and (3) Bence Jones proteins react w ith the assay antibodies differently from the calibration material and from one another. It is concluded that, although there is a qualitative relationship betw een concentrations of Bence Jones proteins and immunoglobulins used for cali­ bration, m easurem ent of absolute levels of Bence Jones proteins using currently available m ethods will lead to inaccuracies resulting from pecu­ liarities betw een the antibody-antigen reaction and because of the spill­ over of polyclonal free light chains into urine. Nevertheless, the data pro­ vides credence for studies suggesting that m easurem ent of the k /A . ratio in serum and urine may be a reliable way to identify Bence Jones proteins by autom ated assays. * This work was supported by funding from the Department of Veteran Affairs. t Address reprint requests to: Stanley S. Levin­ son, Ph.D., Laboratory Service, Department of Vet­ eran Affairs Medical Center, 800 Zorn Avenue, Louisville, KY 40206-1499. Introduction Plasm a ce ll dyscrasia is a process w hereby a m onoclonal popu lation of plasma cells either derived from a single malignant clone or from a nonprolifera­