Quantitative levels of C-reactive protein in cerebrospinal fluid in patients with bacterial meningitis and other conditions.

We measured levels of C-reactive protein (CRP) in the cerebrospinal fluid in 145 children, using a solid-phase radioimmunoassay. The CRP levels in 49 patients with culture-proved bacterial meningitis ranged from 0 to 51,000 ng/ml (median 1460 ng/ml). In 33 patients with aseptic meningitis, values were much lower range 0 to 438 ng/ml; (median 17 ng/ml). In patients with CSF pleocytosis (greater than 10 WBC/microliter), CRP greater than 100 ng/ml was 95% accurate in identifying those with bacterial meningitis. However, a few patients with bacterial meningitis and little or no CSF pleocytosis had low levels of CRP at admission. Among the 63 patients with nonmeningitic conditions, those with bacterial infections frequently (10 of 13 had CRP greater than 100 ng/ml, whereas CRP elevations were infrequent (seven (18%) of 40) in patients with viral infections and other conditions. CRP diffuses into the CSF as readily as other proteins, but in bacterial meningitis the CSF/serum ratio of CRP was lower than that of albumin and IgG. The measurement of CRP in CSF is potentially a very useful diagnostic tool, but certain inherent limitations must be recognized, because some patients may fail to mount a prompt inflammatory response.