Kappa-index: Real-life evaluation of a new tool for multiple sclerosis diagnosis

• Published in: Clinical immunology (Orlando, Fla.) Fla.), 2022-08, Vol.241, p.109066-109066, Article 109066
• Main Authors: Marlas, Mathilde, Bost, Chloé, Dorcet, Guillaume, Delourme, Adrien, Biotti, Damien, Ciron, Jonathan, Renaudineau, Yves, Puissant-Lubrano, Bénédicte
• Format: Article
• Language: English
• Subjects: Cerebrospinal fluid; Diagnosis; Human health and pathology; Kappa free light chain index; Life Sciences; Multiple sclerosis
• ISSN: 1521-6616; 1521-7035
• DOI: 10.1016/j.clim.2022.109066

The intrathecal production of oligoclonal immunoglobulin bands (OCB) is a prognostic factor for multiple sclerosis (MS) evolution in clinically isolated syndrome (CIS) patients and a diagnostic factor for MS. The kappa free light chain (K)-index represents a quantitative automated alternative to OCB. We retrospectively evaluated OCB and K-index results in 274 patients with MS (n = 48) or CIS (n = 29) at diagnosis, non-MS inflammatory central nervous diseases (n = 35), and non-inflammatory central/peripheral nervous diseases (n = 162). Several cut-offs were established: a pathophysiological cut-off (K-index: 3.3) useful for differential diagnosis (negative predictive value for MS >99%), an optimised cut-off (K-index: 9.1) with better sensitivity and equivalent specificity than OCB for the diagnosis of MS, and a high-risk cut-off (K-index: >55.0) allowing prediction of MS (specificity 100%). We developed a scaled interpretation of the K-index and we discuss the usefulness of testing OCB only when the K-index is positive >3.3 to obtain a better specificity. •K-index cut-off 3.3 performed better than OCB (higher sensitivity) for MS diagnosis.•K-index cut-off 9.9 displayed better sensitivity and equivalent specificity than OCB.•High K-index cut-off (>55) performed better than OCB in terms of specificity (100%).•We propose the use of 3 cut-offs allowing a scaled interpretation of K-index.•OCB testing could be avoided when K-index is