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.