Detection of OCB in cerebrospinal fluid (CSF) has been reintroduced in the revised 2017 McDonald’s criteria. Measurement of cKFLC has been demonstrated to be consistent with intrathecal immunoglobulin synthesis and has comparable performance to OCB for the diagnosis of MS.

Validating clinical application of cerebrospinal fluid kappa free light chain (cKFLC) assay as a quantitative alternative to oligoclonal bands (OCB) in multiple sclerosis (MS).

A total of 702 retrospective and 660 prospective paired CSF/serum samples from residual waste samples of physician-ordered OCB testing were obtained and tested for cKFLC. Charts were reviewed by a neurologist blinded to cKFLC results. Specificity and sensitivity for MS diagnosis were evaluated to establish a diagnostic cut-off value for cKFLC in the retrospective cohort, which was then validated in the prospective cohort.

The retrospective and prospective subgroups, respectively, included MS (n=88, 71), non-MS (n=604, 569) and undetermined diagnosis (excluded from analysis, n =8, 17). CSF detection of 2 unique OCB compared with a cKFLC value of 0.1 mg/dL. In the retrospective subgroup, cKFLC vs. OCB sensitivities for the diagnosis of MS were 67.0 vs. 73.6 (p=0.083) and specificities were 86.1 vs. 87.6 (p=0.27,) respectively. cKFLC AUC (95% CI) was 0.766 (0.714 - 0.817), while that for OCB was 0.806 (0.757 - 0.854). In the prospective cohort, cKFLC vs. OCB sensitivity 74.6 (p=1.0) for both and specificities were 87.3 vs 89.6 (p=0.08), respectively.

In comparison to current standards of detecting 2 unique CSF OCB, cKFLC at a value of 0.1 mg/dL showed comparable sensitivity and specificity to support diagnosis of MS. cKFLC is a valid alternative to OCB, offering a standardized quantitative measure, eliminating human error associated with OCB testing and reducing cost and turnover time of testing, with comparable sensitivity and specificity.