In MS Diagnosis, the Case for Κ-FLC Index

Why It Matters

Incorporating κ‑FLC into MS diagnostic guidelines could streamline testing, reduce costs, and improve early detection and risk stratification, potentially accelerating treatment decisions and improving patient outcomes.

Summary

An international expert panel has recommended that the intrathecal kappa free light chain (κ‑FLC) index be added to the next revision of multiple sclerosis (MS) diagnostic criteria as a quantitative, cost‑effective alternative to oligoclonal bands (OCBs). κ‑FLC can be measured rapidly by nephelometry or turbidimetry, offering higher sensitivity than the IgG index (60‑70%) while avoiding the labor‑intensive, rater‑dependent nature of OCB testing. The 2025 McDonald criteria already acknowledge κ‑FLC as interchangeable with OCBs, and emerging data suggest the κ‑FLC index also predicts future inflammatory activity and disability progression. The panel’s consensus underscores κ‑FLC’s diagnostic and prognostic utility, positioning it as a robust biomarker for MS.