Serum C-reactive protein in the differential diagnosis of acute meningitis.

The ability of serum C-reactive protein (S-CRP) to differentiate between acute bacterial and viral meningitis was evaluated in 235 patients, both children and adults. The patients underwent lumbar puncture due to suspected central nervous system (CNS) infection. In patients with bacterial meningitis, 7/60 (12%) had S-CRP concentrations below 50 mg/l. Of these patients, 4 were children below 6 years of age, all with symptoms of meningitis for less than 12 h before admission and 3 adults of whom 1 had symptoms of meningitis for less than 12 h. In patients with viral meningitis, 15/146 (10%) had S-CRP concentrations above 50 mg/l. Only 3 children below 6 years of age with viral meningitis had S-CRP concentration above 20 mg/l, but none exceeded 50 mg/l. An S-CRP value above 50 mg/l in patients with CSF pleocytosis usually indicates bacterial etiology. However, S-CRP values above 50 mg/l may occasionally be seen in viral meningitis. In children younger than 6 years of age a discriminatory level for S-CRP of 20 mg/l can be used to distinguish between bacterial and viral meningitis, but for older patients a discriminatory level of 50 mg/l is more appropriate. If the duration of the illness is less than 12 h, S-CRP concentrations below the discriminatory levels are of limited diagnostic value.