How useful is cerebrospinal fluid lactate estimation in differential diagnosis of meningitis?

Cerebrospinal fluid lactate (CSF) was measured by a rapid enzymatic method in 230 patients admitted with a suspected diagnosis of central nervous system infection. In all untreated cases of bacterial meningitis the levels exceeded 4.3 mmol/l and fell below 3.9 mmol/l in most patients with virus meningitis. We believe values of 3.9-4.3 mmol/l should be considered borderline as occasional CSF samples in cases of virus meningitis yield values in this range. However, distinction between untreated pyogenic meningitis and virus meningitis is rarely problematic in clinical practice, so routine use of the test as an emergency procedure offers no extra advantage. The test is unlikely to be of much help in differentiating partly treated bacterial meningitis from virus meningitis, but it is a valuable additional procedure for differentiating tuberculous meningitis from virus meningitis, highly modified bacterial meningitis and parameningeal septic states.