Clinical comparison of new monoclonal antibody-based nephelometric assays for free light chain kappa and lambda to polyclonal antibody-based assays and immunofixation electrophoresis

摘要

Background: New monoclonal antibody-based assays for serum-free light chains (FLC) have become available. Methods: In a clinical study with 541 patients, the new N Latex FLC assays were compared with the Freelite (TM) FLC assays and immunofixation electrophoresis (IF). Results: Comparison of the different FLC kappa (kappa) assays showed a slope of 0.99 with a deviation of 5.0%, r(s)=0.92, for FLC lambda (lambda) a slope of 1.22, deviation 13.8%, r(s)=0.90 and for the kappa/lambda ratio a slope of 0.72, deviation -4.6%, r(s)=0.72. The concordance for the FLC kappa assays was 91%, for FLC lambda 85% and kappa/lambda ratio 95%. The clinical sensitivity and specificity of the kappa/lambda ratios in the study were comparable: 60% and 99% for the N Latex FLC assay and 61% and 97% for the Freelite (TM) assay. In IF-FLC positive samples, the N Latex FLC kappa/lambda ratio scored 20/23 (87%) samples outside the reference range and Freelite (TM) 21/23 (91%). For IF-FLC negative samples, N Latex FLC assay kappa/lambda ratio scored 338/350 (97%) within the reference range and Freelite (TM) scored 332/350 (95%). Conclusions: The concordance scores and the clinical sensitivity and specificity of the new N Latex FLC assays and Freelite (TM) assays appeared comparable, but there are some differences in measurement of concentrations between the methods