The value of initial laboratory investigations in the management of meningitis.

The results of cerebrospinal fluid (CSF) examination and other initial laboratory investigations have been analysed in one hundred and forty-nine patients with meningitis. The CSF differential leucocyte count clearly distinguished between bacterial and viral meningitis in 92 per cent of patients evaluated: CSF glucose and protein concentrations were less predictive by comparison. CSF glucose values were particularly unreliable because of hyperglycaemia in patients with bacterial meningitis and predictive accuracy increased when CSF levels were expressed as a percentage of blood glucose concentration. Results were not influenced by the age of the patients, and laboratory evidence of bacterial infection did not appear to be masked by prior antimicrobial therapy. A management algorithm based on the results of initial tests was applied retrospectively to the patients in whom Gram-stained CSF did not reveal bacteria. The algorithm indicated immediate antimicrobial therapy for all thirty patients with pyogenic infections, and for only one of sixty-three patients with a final diagnosis of viral meningitis.