From the Guidelines
Normal CSF sugar content is between 2.6-4.5 mmol/L, and normal protein content is less than 0.4 g/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.
Key Points to Consider
- The CSF glucose level is approximately two-thirds of the blood glucose level, and the CSF:plasma glucose ratio is typically greater than 0.66 in normal individuals 1.
- The protein content in normal CSF is kept low by the blood-brain barrier, which restricts the passage of larger molecules.
- Abnormally low CSF glucose levels may indicate bacterial meningitis, fungal infections, or certain cancers, while elevated protein levels can suggest infection, multiple sclerosis, Guillain-Barré syndrome, or other neurological disorders.
Diagnostic Parameters
- CSF glucose levels: 2.6-4.5 mmol/L
- CSF protein levels: less than 0.4 g/L
- CSF:plasma glucose ratio: greater than 0.66
Clinical Interpretation
When interpreting CSF results, it's essential to consider these values in relation to the patient's blood glucose level and clinical presentation, as variations can provide valuable diagnostic information about central nervous system pathologies 1.
Important Considerations
- A CSF glucose level above 2.6 mmol/L is unlikely to be associated with bacterial meningitis 1.
- A CSF protein level less than 0.6 g/L makes bacterial disease unlikely 1.
- CSF lactate levels can also be used to distinguish between bacterial and viral meningitis, with a cut-off of 35 mg/dl having the best sensitivity 1.
From the Research
Normal CSF Sugar Content
- The normal cerebrospinal fluid (CSF) glucose level is influenced by the blood glucose level 2
- CSF glucose levels increased with blood glucose levels at 6,5,4,3,2,1, and 0 h before lumbar puncture 2
- Age-specific reference ranges for CSF glucose were defined as 5-95(th) percentile ranges, with 5(th) percentile values ranging from 1.8 to 2.9 mmol/L and 95(th) percentile values ranging from 3.8 to 5.6 mmol/L 3
- The CSF/blood glucose ratio range was 0.35-0.95 at 0-6 h before lumbar puncture in patients with normal glucose metabolism 2
- The CSF/average blood glucose ratio range was 0.43-0.74 in patients with normal glucose metabolism 2
Normal CSF Protein Content
- There is no direct information about normal CSF protein content in the provided studies
- However, some studies mentioned that the CSF samples were included if they had normal total protein content 4, 5
- One study excluded CSF samples with elevated concentrations of total protein 3
CSF Glucose and Protein Measurement
- CSF glucose and lactate levels can be used to distinguish between acute bacterial meningitis and viral meningitis 6
- The CSF lactate level was 4-fold higher in the acute bacterial meningitis group than in the acute viral meningitis and control groups 6
- The CSF:SGlu ratio is similar in ventricular and lumbar compartments, and depends mainly on time to laboratory processing and absolute serum glucose levels 4
- Cut-off values for normal CSF/SGlu ratio defined as the 5th percentile were 0.5 for patients with serum glucose concentrations <100 mg/dL, 0.4 for those with a glucose level of 100-149 mg/dL, and 0.3 for serum glucose concentrations ≥150 mg/dL 5