Cerebrospinal fluid interleukin-6 and its diagnostic value in the investigation of meningitis

We examined the measurement and the diagnostic value of cerebrospinal fluid interleukin-6 (CSF IL-6) in meningitis. The cytokine was measured by bioassay (B9 hybridoma cell line) and by immunoassay (in-house radioimmunoassay). We compared the diagnostic value of CSF IL-6 determination with that of other biochemical markers of meningitis. Although there was significant correlation between bioactive and immunoactive IL-6 (r = 0·724, P < 0·001), results were frequently different with biological/immunological ratios ranging from 0·2 to 24·3 (mean 4·6). Gel permeation chromatography suggested that the discrepancy in biological and immunological activities was not due to molecular heterogeneity, but may be explained by the presence of a synergistic factor. Interleukin-6 concentration was markedly elevated in CSF from most patients with bacterial meningitis compared to patients with viral meningitis and those without evidence of infection. However, low IL-6 levels by radioimmunoassay did not exclude bacterial meningitis (sensitivity 86%). CSF total protein and CSF glucose were significantly different between all three groups, but there was no significant difference in lactate concentration between virally infected and normal CSF, both of which had lower lactate concentrations than those in bacterial infection. CSF IL-6 measurement had greater sensitivity, specificity and predictive value than these other biochemical markers, and hence a rapid assay for IL-6 in CSF may contribute to the early diagnosis of bacterial infection.