Serum immunoglobulin free light chains in patients with monoclonal gammapathies

Serum concentrations of κ- and λ-free light chains and their ratios were compared in 126 patients with monoclonal gammapathies (age 23-80 years) and 60 normal subjects (25-82 years). The main group included patients with intact immunoglobulin multiple myeloma, Bence Jones multiple myeloma, nonsecreting multiple myeloma, plasmocytoma, and monoclonal gammapathy of unknown origin. The accuracy of the method was evaluated by the analysis of 3 serum specimens with different concentrations of κ- and λ-free light chains. The variability of the method did not surpass the coefficient of variations permissible for this kind of analysis (10%). The new immunochemical method is characterized by high analytical sensitivity 100-fold surpassing that of electrophoretic methods. High concentrations of free light chains were most often found in the sera of patients with multiple myeloma with intact immunoglobulin secretion, Bence Jones multiple myeloma, and plasmocytoma. The diagnostic sensitivity of measurements of serum free light chains by the immunoturbidimetric method attained 90.5%. Combination of this method with serum protein electrophoresis and immunofixation resulted in detection of monoclonal gammapathy in 98.8% cases. These data indicate high specificity and analytical and diagnostic sensitivity of the immunoturbidimetric method for measurement of serum free light chains.