Cerebrospinal fluid levels of lysozyme, IgM and C-reactive protein in the identification of bacterial meningitis.

Lysozyme (LZM), immunoglobulin M (IgM) and C-reactive protein (CRP) levels were determined in cerebrospinal fluid (CSF) from patients classified on the basis of clinical and laboratory findings into three groups: bacterial meningitis (n = 33), lymphocytic meningitis (n = 21) and controls (n = 54). IgM and CRP levels were determined by enzyme-linked immunosorbent assay (ELISA) and LZM by the lysoplate method. Discriminant analysis demonstrated that 93.94% (31/33) and 96.97% (32/33) of patients with bacterial meningitis were correctly classified on the basis of CSF determinations of IgM and LZM, respectively. However, the measurement of CRP levels in CSF correctly classified 100% of these patients (33/33), thus representing a useful additional marker for the screening of bacterial meningitis. Moreover, no more than 4% (3/75) of patients were incorrectly classified as belonging to the bacterial group on the basis of the CRP test. Thus, CRP titres less than or equal to 80 identify cases belonging to one of the non-bacterial groups, whereas titres greater than or equal to 640 classify the bacterial group, with a very low chance of misclassification. The authors recommend that CSF IgM or LZM levels be also measured for patients with CSF CRP titres of 160 and 320, for a more accurate diagnosis. The probability of these cases being of bacterial aetiology, as calculated from the combined results of these measurements, is presented.