What Laboratory Testing May Be Helpful in Distinguishing Bacterial from Viral Meningitis?
Determination of Lactate Concentration
Measurement of CSF lactate concentration is not recommended for patients with suspected community-acquired bacterial meningitis (D-III)
However, measurement of CSF lactate concentrations was found to be superior to use of the ratio of CSF to blood glucose for the diagnosis of bacterial meningitis in postoperative neurosurgical patients, in which a CSF concentration of 4.0 mmol/ L (36 mg/dL) was used as a cutoff value for the diagnosis. The sensitivity was 88%, the specificity was 98%, the positive predictive value was 96%, and the negative predictive value was 94%. CSF lactate concentrations may be valuable in this subgroup of patients, in whom the usual CSF findings--elevated white blood cell (WBC) counts (total and differential), positive Gram stain results, diminished glucose concentrations, and elevated protein concentrations--are neither sensitive nor specific to reliably distinguish bacterial from a nonbacterial meningeal syndrome. Therefore, in the postoperative neurosurgical patient, initiation of empirical antimicrobial therapy should be considered if CSF lactate concentrations are > 4.0 mmol/L, pending results of additional studies (B-II).