Cerebrospinal fluid C-reactive protein in meningitis: diagnostic value and pathophysiology.

We examined the diagnostic value of C-reactive protein (CRP) in cerebrospinal fluid (CSF) on initial lumbar puncture in a prospective study including 126 patients (30 neonates, 96 infants and children) suspected of having meningitis. Twenty patients were considered to have bacterial and 25 were considered to have viral meningitis. In infants and children, a retrospectively chosen cut-off CRP titre of 4 (i.e. approximately equal to 0.4 mg/l CRP) had a sensitivity of 100% and a specificity of 94% for differentiating bacterial meningitis from both viral meningitis and normal. It was a more sensitive and selective test for differentiating bacterial from viral meningitis on initial CSF examination than was the CSF leucocyte count, glucose concentration or protein concentration. In neonates, no such cut-off CRP titre could be found, presumably due to the immaturity of the blood-CSF-barrier (B1-CSF-B) during the first weeks of life. In a parallel study including a non-selected group of 13 infants and children (4 without, 9 with bacterial meningitis), the serum/CSF CRP concentration ratios were determined and inserted in the individual B1-CSF-B diagrams according to Felgenhauer. The results were fully consistent with the hypothesis that the CRP concentration in CSF reflects the normal permeability characteristics of the B1-CSF-B, or the degree of its impairment. Based on our results, we recommend the CSF CRP estimation in the routine evaluation of infants and children suspected of having meningitis.