From the Guidelines
Normal cerebrospinal fluid (CSF) glucose levels typically range from 2.6 to 4.5 mmol/L, as indicated in the UK Joint Specialist Societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults 1. This range is essential for clinicians to understand, as CSF glucose levels can help differentiate between various causes of meningitis.
Key Points to Consider
- The CSF glucose level should be interpreted in the context of the plasma glucose level, as it is approximately two-thirds of the blood glucose concentration 1.
- A CSF:plasma glucose ratio of greater than 0.66 is considered normal, while a ratio below this threshold may indicate bacterial meningitis 1.
- When interpreting CSF glucose values, it is crucial to measure blood glucose simultaneously, as the CSF glucose level should be approximately 60-70% of the blood glucose level.
- Low CSF glucose (hypoglycorrhachia) can indicate bacterial meningitis, fungal infections, carcinomatous meningitis, or subarachnoid hemorrhage, while elevated CSF glucose is less common but may occur with hyperglycemia.
Clinical Implications
- Clinicians should be aware of the normal range of CSF glucose levels to accurately diagnose and manage patients with suspected meningitis.
- The glucose concentration in CSF reflects the balance between transport from blood and utilization by brain tissue, with equilibration taking about 2 hours after changes in blood glucose levels.
- CSF lactate levels can also be used to distinguish between bacterial and viral meningitis, with a high sensitivity and specificity if antibiotics have not been given beforehand 1.
From the Research
Normal CSF Glucose Levels
- The normal CSF glucose levels can be determined by examining the correlation between blood and CSF glucose levels in patients with normal and abnormal glucose metabolism 2.
- A study found that in patients with normal glucose metabolism, the CSF/blood glucose ratio range was 0.35-0.95 at 0-6 hours before lumbar puncture, and the CSF/average blood glucose ratio range was 0.43-0.74 2.
- Another study reported a mean CSF glucose value of 98.97 ± 61.10 mg/dL using the conventional laboratory technique, and 109.59 ± 67.85 mg/dL using a glucometer 3.
- The CSF glucose level is influenced by the blood glucose level 6 hours before lumbar puncture, and direct measurement of the CSF glucose level can be used to determine whether the CSF level is normal in patients with normal glucose metabolism 2.
CSF/Blood Glucose Ratio
- The CSF/blood glucose ratio can be used as an indicator for bacterial meningitis, with an optimal cut-off of 0.36, sensitivity of 92.9%, specificity of 92.9%, and area under the curve of 0.97 4.
- The CSF/serum glucose ratio had a high area under the curve (0.843) for discriminating bacterial meningitis, and can be used to predict bacterial meningitis as well as mortality 5.
- The CSF/serum glucose ratio is a useful diagnostic indicator of bacterial meningitis, especially in cases where no microorganisms can be cultured 4.