Determination of kFLC and K Index in cerebrospinal fluid: A valid alternative to assessintrathecal immunoglobulin synthesis

•Kappa free light chains (kFLCs) were increased in early multiple sclerosis (MS).•CSF/serum ratio of kFLC was increased in MS.•kFLC Index seems to be a good tool in MS diagnoses.

Intrathecal immunoglobulin synthesis is observed in several disorders of the central nervous system, but its detection by current laboratory tests is relatively insensitive and operator depending. We assessed the diagnostic accuracy of a nephelometric assay for k free light chain determination in cerebrospinal fluid and serum. The patients were grouped according to clinical and laboratory criteria. ROC curves for all methods were performed to find the best cut-off value. kFLC Index seems to be more accurate than other parameters. Our data indicate that nephelometric assay for kFLCs in CSF reliably detect intrathecal immunoglobulin synthesis and discriminate multiple sclerosis patients.