Serum and urine light chain levels in benign monoclonal gammapathies, multiple myeloma and Waldenström's macroglobulinaemia.

Immunochemical quantitative determinations of both serum and urine free light chains were carried out in seventy-five subjects with a serum M-component. Diagnoses were benign monoclonal gammapathy (BMG) in thirty-four cases, multiple myeloma (MM) in thirty-one and Waldenström's macroglobulinaemia (WM) in ten. The single radial immunodiffusion test was used throughout, employing a special rabbit anti-Bence Jones antiserum, made specific for hidden antigenic sites of light chains by suitable absorptions. The smallest amount of free light chains which could be detected by this method was 0·02 mg/ml for both κ and λ chains. In MM 84% of sera and 87% of urine revealed detectable amounts of Bence Jones protein, whereas in WM the corresponding figures were 80% for both sera and urines. The values ranged considerably from case to case, and tended to be higher in the urines. In BMG a definitely lower incidence of free light chains was recorded (in the sera: 35·2%; in the urines: 41·1%), and the levels were restricted to a much narrower range. The significance of these findings is briefly discussed.