Cerebrospinal fluid/blood glucose ratio as an indicator for bacterial meningitis

Background

Bacterial meningitis is an emergent disease requiring prompt diagnosis and treatment with appropriate antimicrobials. Although the lumbar puncture is widely used as a diagnostic tool for bacterial meningitis, it remains unclear which value in cerebrospinal fluid (CSF) analysis in emergency laboratory tests precisely predicts the presence of bacterial meningitis.

Methods

This is a single-center, retrospective review of medical records to determine which emergency laboratory CSF test results are useful for predicting bacterial meningitis. The diagnosis of meningitis is made when the white blood cell count in CSF exceeds 5 cells/μL, while the diagnosis of bacterial meningitis additionally requires the growth of a pathogen from a CSF culture or the identification of a pathogen in Gram staining of CSF specimen.

Results

We identified 15 patients with bacterial meningitis and 129 patients with aseptic meningitis. While neutrophil-predominant pleocytosis and a decreased glucose level in CSF can predict the presence of bacterial meningitis, the CSF/blood glucose ratio is more precise (optimal cut-off = 0.36, sensitivity = 92.9%, specificity = 92.9%, area under the curve = .97) even after administration of antimicrobials prior to examination in the emergency department.

Conclusion

This study suggests that the CSF/blood glucose ratio may be a better single indicator for bacterial meningitis. Since the CSF glucose and blood glucose values are promptly and easily obtained from a lumbar puncture, the CSF/blood glucose ratio should be considered as a timely diagnostic indicator of bacterial meningitis. It may also help exclude the diagnosis of bacterial meningitis especially in cases in which no microorganisms can be cultured.