Cerebrospinal fluid free kappa light chains versus IgG findings in neurological disorders: qualitative and quantitative measurements.

In this study free kappa light chains in cerebrospinal fluid (CSF) were determined both by an affinity mediated capillary blotting technique after isoelectric focusing (IEF) in agarose gel and by a quantitative enzyme linked immunosorbent assay (ELISA). The free kappa results were compared with the IgG findings in 4 neurological patient groups with a distinct CSF IgG pattern: (1) CSF without oligoclonal IgG bands, (2) CSF with serum derived IgG bands, (3) CSF restricted IgG bands and (4) CSF restricted and serum derived IgG bands. Oligoclonal free kappa bands are nearly absent in CSF of groups 1 + 2, and present in 88% of group 3 and 84% of group 4 patients. We could also establish free kappa indices from specimens in the 4 groups in analogy to IgG indices. Group 1 had a median free kappa index of 1.1, group 2: 1.0 and groups 3 + 4: 10.0. The correspondence between immunoblot and index findings for free kappa is better than for IgG. Free kappa index is more sensitive but somewhat less specific than IgG index for establishing intrathecal immune production.