[Usefulness of the kappa index in the diagnosis of multiple sclerosis and validation of reference values in the Community of Aragon].

INTRODUCTION: Detection of oligoclonal bands (OCB) in CSF is essential in the diagnosis of multiple sclerosis (MS). Kappa-index is a promising biomarker, with sensitivity and sensibility values comparable to those of OCB. Our objective was to investigate kappa-index utility in the diagnosis work-up for MS and to determine the optimal cut-off point for our population.

MATERIAL AND METHODS: Observational study of consecutive samples received in the Immunology lab department in a third level hospital between January 2019 to June 2020. Kappa-index and IgG index were measured. ROC analysis for screening of OCB and for diagnosis of MS was conducted. Sensibility, specificity and the optimal cut-off points were determined.

RESULTS: 181 samples were included (59.7% females; age, 47.62 ± 17.8 years). Patients in the EM group presented significantly higher kappa-index level than patients without an EM diagnosis (66.62 versus 0.02; p < 0.001). ROC analysis reported a better area under the curve for the kappa-index than the IgG index for the detection of BOC (0.93 versus 0.83; p < 0.002) and the diagnosis of EM (0.91 versus 0.83; p < 0.021). An optimal cut-off point of 5.02 was determined for the detection of BOC (sensibility and specificity, 0.92) and of 7.58 for the diagnosis of EM (sensibility, 0.85; specificity, 0.94).

CONCLUSIONS: Kappa-index is an useful biomarker in the diagnosis of MS. Its specificity and sensibility are superior to the IgG index. The optimal cut-off point has yet to be determined, but for our population a cut-off of 5.02 seems reasonable.