Assessment of the analytical performance and the sensitivity of serum free light chains immunoassay in patients with monoclonal gammopathy

Objectives:A new immunoassay which quantifies Kappa, Lambda free light chains (FLC) and a ratio of Kappa to Lambda FLC has been reported to be sensitive for detecting a variety of FLC diseases. We assessed the analytical criteria and the diagnostic performance of this immunoassay in patients who present a monoclonal gammopathy.Design and methods:Quantification of FLC, serum protein electrophoresis (SPE) and immunofixation (IFE) were performed on patients who present a monoclonal gammopathy of undetermined significance (MGUS), an intact immunoglobulin multiple myeloma (IIMM) or a light chain multiple myeloma (LCMM).Results:The monoclonal component was identified by IFE in the sera of all patients. Based on the diagnostic reference range, the ratio of Kappa to Lambda FLC was abnormal in 25% of the tested population, compared to 94% for SPE in MGUS patients. For IIMM and LCMM, the FLC ratio was abnormal in 70% and 100% of the population, compared to 85% and 40% for SPE, respectively.Conclusion:SPE and IFE have a higher sensitivity for identifying MGUS and IIMM.