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.
Key words. Biomarker. Cerebrospinal fluid. Demyelinating diseases. Kappa-index. Multiple sclerosis. Oligoclonal bands.