Clinical Use of κ Free Light Chains Index as a Screening Test for Multiple Sclerosis

Objective: To assess the usefulness of the kappa free light chain index (kappa FLCi) as a screening test to identify patients with suspected MS. Methods: The study included 56 patients with a request to test for oligoclonal bands (OCBs). OCBs were detected by isoelectric focusing, followed by immunofixation. Cerebrospinal fluid (CSF) and serum kappa FLC were measured by a turbidimetric assay. Also, the kappa FLC index (kappa FLCi) was calculated. Results: CSF kappa FLC levels and kappa FLCi were significantly higher in patients with multiple sclerosis (MS) than in patients with other neurological diseases (NDs; P < .001 and P < .001, respectively). At the cutoff value of 2.9, the kappa FLCi detected MS with sensitivity of 97% and specificity of 65%. Overall, 92% patients with kappa FLCi of 2.9 or greater and who had tested positive for OCBs were diagnosed as having MS. Conclusion: Our findings support the use of kappa FLCi as a screening test when MS is suspected, followed by OCB detection as a confirmatory test for the diagnosis of MS.