Leurs, C.E. (56866079400)C.E. (56866079400)LeursTwaalfhoven, H.A.M. (26533533200)H.A.M. (26533533200)TwaalfhovenLissenberg-Witte, B.I. (57204744042)B.I. (57204744042)Lissenberg-Wittevan Pesch, V. (15847200900)V. (15847200900)van PeschDujmovic, I. (6701590899)I. (6701590899)DujmovicDrulovic, J. (55886929900)J. (55886929900)DrulovicCastellazzi, M. (57190160648)M. (57190160648)CastellazziBellini, T. (7004337741)T. (7004337741)BelliniPugliatti, M. (6603827112)M. (6603827112)PugliattiKuhle, J. (8937520800)J. (8937520800)KuhleVillar, L.M. (35518965300)L.M. (35518965300)VillarAlvarez-Cermeño, J.C. (7004605927)J.C. (7004605927)Alvarez-CermeñoAlvarez-Lafuente, R. (13411081600)R. (13411081600)Alvarez-LafuenteHegen, H. (57202373490)H. (57202373490)HegenDeisenhammer, F. (7004758773)F. (7004758773)DeisenhammerWalchhofer, L.M. (57194580116)L.M. (57194580116)WalchhoferThouvenot, E. (35325407800)E. (35325407800)ThouvenotComabella, M. (6701491362)M. (6701491362)ComabellaMontalban, X. (7007177960)X. (7007177960)MontalbanVécsei, L. (35452449900)L. (35452449900)VécseiRajda, C. (6603645376)C. (6603645376)RajdaGalimberti, D. (6701617660)D. (6701617660)GalimbertiScarpini, E. (57210771033)E. (57210771033)ScarpiniAltintas, A. (7006317905)A. (7006317905)AltintasRejdak, K. (8284992700)K. (8284992700)RejdakFrederiksen, J.L. (7102315536)J.L. (7102315536)FrederiksenPihl-Jensen, G. (56568478300)G. (56568478300)Pihl-JensenJensen, P.E.H. (57214664093)P.E.H. (57214664093)JensenKhalil, M. (55628524072)M. (55628524072)KhalilVoortman, M.M. (57195917900)M.M. (57195917900)VoortmanFazekas, F. (7102945505)F. (7102945505)FazekasSaiz, A. (56213393300)A. (56213393300)SaizLa Puma, D. (56422282100)D. (56422282100)La PumaVercammen, M. (6602461163)M. (6602461163)VercammenVanopdenbosch, L. (6602558181)L. (6602558181)VanopdenboschUitdehaag, B.M.J. (57243388200)B.M.J. (57243388200)UitdehaagKillestein, J. (7004423164)J. (7004423164)KillesteinBridel, C. (6508071655)C. (6508071655)BridelTeunissen, C. (6701704380)C. (6701704380)Teunissen2025-06-122025-06-122020https://doi.org/10.1177/1352458519845844https://www.scopus.com/inward/record.uri?eid=2-s2.0-85065731162&doi=10.1177%2f1352458519845844&partnerID=40&md5=8d7a613546265a64ae9b2f8981a1a915https://remedy.med.bg.ac.rs/handle/123456789/4826Objective: To validate kappa free light chain (KFLC) and lambda free light chain (LFLC) indices as a diagnostic biomarker in multiple sclerosis (MS). Methods: We performed a multicenter study including 745 patients from 18 centers (219 controls and 526 clinically isolated syndrome (CIS)/MS patients) with a known oligoclonal IgG band (OCB) status. KFLC and LFLC were measured in paired cerebrospinal fluid (CSF) and serum samples. Gaussian mixture modeling was used to define a cut-off for KFLC and LFLC indexes. Results: The cut-off for the KFLC index was 6.6 (95% confidence interval (CI) = 5.2–138.1). The cut-off for the LFLC index was 6.9 (95% CI = 4.5–22.2). For CIS/MS patients, sensitivity of the KFLC index (0.88; 95% CI = 0.85–0.90) was higher than OCB (0.82; 95%CI = 0.79–0.85; p < 0.001), but specificity (0.83; 95% CI = 0.78–0.88) was lower (OCB = 0.92; 95% CI = 0.89–0.96; p < 0.001). Both sensitivity and specificity for the LFLC index were lower than OCB. Conclusion: Compared with OCB, the KFLC index is more sensitive but less specific for diagnosing CIS/MS. Lacking an elevated KFLC index is more powerful for excluding MS compared with OCB but the latter is more important for ruling in a diagnosis of CIS/MS. © The Author(s), 2019.biomarkersCSFKFLCMultiple sclerosisOCB