The clinical value of rapid C-reactive protein measurement in cerebro-spinal fluid.

C-Reactive protein (CRP) has been measured in 90 consecutive CSF specimens using both latex agglutination and an immunoradiometric assay (IRMA). In the 60 CSF specimens otherwise normal by standard biochemical and microbiological criteria, the median CRP level was 32 micrograms/l (95% confidence limits, 0-108 micrograms/l) and in the remaining abnormal specimens the median level was 176 micrograms/l (95% confidence limits, 110-325 micrograms/l, p = 0.001). C-Reactive protein was detected by a commercial latex agglutination kit at a level of approximately 120 micrograms/l and all significant CNS bacterial infections were positive (7 bacterial meningitis, 2 infected shunts). In addition, viral encephalitis, extensive intracranial malignancy and subarachnoid haemorrhage gave positive agglutinations, but not in every case. A further nine specimens with a minor elevation of CRP level were detected by IRMA (median 76 micrograms/l), but this was of little practical significance. We have shown that normal CSF C-reactive protein levels are very low and we conclude that latex agglutination set at a sensitivity of 120 micrograms/l, although only semi-quantitative, is a rapid and useful method to assess CSF C-reactive protein in routine clinical practice and, when positive, is strong supporting evidence for bacterial infection.