[Differentiating bacterial from viral meningitis: contribution of nonmicrobiological laboratory tests].

In most cases, differentiating viral from bacterial meningitis is relatively easy, based on clinical examination, CSF appearance and results of CSF examination (cytology, biochemistry and Gram stain). However, in about 20% of cases, this diagnosis may be difficult. For such cases, additional non-microbiological tests may be helpful. CSF lactate level is a good predictor of bacterial meningitis for values greater than 3.5 mmol/l. Serum procalcitonin is effective to discriminate between bacterial and viral meningitis, using a threshold between 1 and 2 ng/ml, although this parameter may fail in individual situations. Accurate diagnosis scores or models have been validated and may be used in routine clinical practice, especially in emergency rooms, both for adults and children to help identify patients with a very low probability of bacterial meningitis in whom antibiotic may thus be avoided.