Serum Free Light Chain Assay and Kapa/Lamtha Ratio: Performance in Patients With Monoclonal Gammopathy-High False Negative Rate for Kapa/Lamtha Ratio

Gurmukh Singh


Background: Serum free light chain assay (SFLCA) and kapa/lamtha ratio, and protein electrophoretic methods are used in the diagnosis and monitoring of monoclonal gammopathies.

Methods: Results for serum free light chains, serum and urine protein electrophoreses and immunofixation electrophoreses in 468 patients with a diagnosis of monoclonal gammopathy were compared. The results of the two methods were graded as concordant, non-concordant or discordant with the established diagnoses to assess the relative performance of the methods. Results ofkapa/lamtha ratio in samples with monoclonal protein detectable by electrophoretic methods were also analyzed.

Results: Protein electrophoreses results were concordant with the established diagnoses significantly more often thankapa/lamtha ratio. The false negative rate forkapa/lamtha ratio was higher than that for electrophoretic methods. Kapa/lamtha ratio was falsely negative in about 27% of the 1,860 samples with detectable monoclonal immunoglobulin. The false negative rate was higher in lesions with lambda chains (32%) than those with kappa chains (24%). The false negative rate forkapa/lamtha ratio was over 55% in samples with monoclonal gammopathy of undetermined significance. Even at first encounter, the false negative rates forkapa/lamtha ratios for monoclonal gammopathy of undetermined significance, smoldering myeloma and multiple myeloma were 66.98%, 23.08%, and 30.15%, respectively, with false negative rate for lambda chain lesions being higher.

Conclusions: Electrophoretic studies of serum and urine are superior to SFLCA and kapa/lamtha ratio. Abnormalkapa/lamtha ratio,per se, is not diagnostic of monoclonal gammopathy. A normalkapa/lamtha ratio does not exclude monoclonal gammopathy. False negative rates for lesions with lambda chain are higher than those for lesions with kappa chains. Electrophoretic studies of urine are underutilized. Clinical usefulness and medical necessity of SFLCA andkapa/lamtha ratio is of questionable value in routine clinical testing.

J Clin Med Res. 2017;9(1):46-57


Monoclonal gammopathy; Serum free light chain assay; Kappa/lambda ratio; Serum protein electrophoresis; Serum protein immunofixation electrophoresis; Urine protein electrophoresis; Urine protein immunofixation electrophoresis

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