From the Guidelines
In bacterial meningitis, CSF glucose levels are typically decreased, while protein levels are elevated, and these changes are crucial for diagnosing and guiding treatment decisions. The combination of low glucose and high protein levels in the cerebrospinal fluid (CSF), along with other diagnostic tests such as CSF lactate concentration, PCR, and Gram stain, helps differentiate bacterial meningitis from other types of meningitis 1. According to the ESCMID guideline, the diagnostic accuracy of CSF lactate is better than that of CSF WBC count, and PCR has incremental value compared to CSF culture and Gram stain 1.
Key diagnostic features of bacterial meningitis include:
- Low CSF glucose levels (less than 40 mg/dL or less than 50% of serum glucose)
- Elevated CSF protein levels (usually greater than 100 mg/dL)
- Elevated white blood cell counts (predominantly neutrophils)
- Positive CSF culture, PCR, or Gram stain results
The degree of glucose depression and protein elevation often correlates with infection severity, with more dramatic changes indicating more severe infections 1. Normal CSF glucose is approximately 60-80% of serum glucose levels, and normal protein ranges from 15-45 mg/dL, so significant deviations from these values warrant prompt attention and treatment. The yield of CSF culture decreases when a patient is treated with antibiotics before lumbar puncture, highlighting the importance of prompt diagnosis and treatment 1.
In clinical practice, it is essential to consider these diagnostic features and test results to guide initial empiric antibiotic therapy decisions while awaiting culture results, as delays in treatment can significantly impact morbidity, mortality, and quality of life.
From the Research
Glucose and Protein Levels in CSF for Bacterial Infection Diagnosis
- The diagnosis of bacterial meningitis can be made by analyzing cerebrospinal fluid (CSF) glucose and protein levels, among other factors 2, 3, 4.
- A decreased glucose level in CSF can predict the presence of bacterial meningitis, and the CSF/blood glucose ratio is a more precise indicator (optimal cut-off=0.36, sensitivity=92.9%, specificity=92.9%) 2.
- A CSF-blood glucose ratio of 0.4 or less is also a reliable indicator for bacterial meningitis (likelihood ratio [LR], 18; 95% CI, 12-27) 3.
- Other studies have found that a CSF/blood glucose ratio calculated from a bedside glucometer can be used to detect bacterial infection in the CSF immediately after CSF sampling, with an optimal cut-off of 0.46, sensitivity of 94.1%, and specificity of 91% 4.
Protein Levels in CSF
- While protein levels in CSF are not directly mentioned as a diagnostic indicator for bacterial meningitis in the provided studies, it is known that bacterial meningitis can cause an increase in protein levels in CSF.
- However, the provided studies do not specifically address the role of protein levels in CSF for diagnosing bacterial meningitis.
Diagnostic Techniques and Treatment
- Lumbar puncture with CSF analysis is a recommended diagnostic tool for bacterial meningitis 5, 6.
- Empiric antimicrobial therapy should be started promptly in patients with suspected bacterial meningitis, and concomitant therapy with dexamethasone may improve morbidity and mortality 5, 6.
- Vaccination against common pathogens that cause bacterial meningitis is also recommended to prevent the disease 5, 6.