Serum Free Light Chain Quantification Testing: Comparison of Two Methods for Disease Monitoring

Background: Levels of free immunoglobulin light chains in serum and urine are a sensitive measure of dysregulated immunoglobulin synthesis. The development of an assay for free light chains in serum was a major advance in laboratory testing for monoclonal gammopathies. The original assay by The Binding Site, called Freelite®, has been in common use in laboratory monitoring of monoclonal gammopathies. Two clinical entities, myeloma-defining condition and light chain-predominant multiple myeloma, rely on quantitative measurements of serum free light chains. Methods: Using polyclonal antisera specific to free light chains, Diazyme Laboratories developed a latex immunoturbidimetric assay for quantification of human kappa and lambda serum free light chains. We evaluated the Diazyme assay by comparing the results of kappa and lambda free light chain quantification, and kappa/lambda ratio with the results on the same specimens by the Freelite method. We also compared the correlation of the 2 methods to evaluate response to treatment and to changes in clinical status of patients with multiple myeloma. Results: The results of Freelite and Diazyme methods are comparable. There was no statistically significant difference in the performance of the 2 assays for quantification of light chains, kappa/lambda ratio, or correlation of clinical parameters from patients with multiple myeloma at various stages of monitoring the disease in 2 geographically diverse laboratory and clinical environments. Conclusions: The Diazyme method is comparable to Freelite and provides an opportunity to add the test to front-end automation and improvement in efficiency of the assay.