Cerebrospinal fluid free kappa light chains and kappa index perform equal to oligoclonal bands in the diagnosis of multiple sclerosis.

Background Detection of intrathecal immunoglobulin G (IgG) synthesis by gold standard oligoclonal bands (OCB) or IgG index remains an integral part of multiple sclerosis (MS) diagnostics, although both methods have weaknesses. Emerging evidence suggests that automated detection of free light chains (FLC) in the cerebrospinal fluid (CSF) has diagnostic performance equal to OCB. The objective of this study was to compare the diagnostic performance of CSF FLC with OCB and IgG index in a large cohort of Scandinavian patients referred for MS evaluation. Methods We prospectively included 230 patients suspected for MS. They are composed of patients with MS (n=96), clinically isolated syndrome (n=37), other neurological diseases (OND, n=31) and symptomatic controls (SC, n=66). CSF and serum samples were analyzed for kappa and lambda FLC, OCB and IgG index. Diagnostic performance was evaluated by receiver operating characteristic (ROC) analysis. Results Both the absolute concentration of CSF-kappa and the kappa index had excellent MS diagnostic performances with ROC area under the curve of 0.93 and 0.94 (MS vs. SC+OND). At the 0.42 mg/L cutoff, CSF-kappa had sensitivity and specificity of 93.8% and 85.6%, whereas sensitivity and specificity for OCB was 82.3% and 93.8% (72.9% and 95.9% for IgG index at cutoff 0.64). CSF-lambda and lambda index performed inferior to CSF-kappa and kappa index. Conclusions CSF-kappa and kappa index represent automated, rapid and low-cost alternatives to OCB. Using merely the absolute concentration of CSF-kappa is a logistic advantage in the clinical laboratories.