What do a cerebrospinal fluid glucose of 112 mg/dL and protein of 30 mg/dL indicate?

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Last updated: September 10, 2026 • View editorial policy

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Normal CSF Values - No Evidence of Bacterial Meningitis

These CSF values (glucose 112 mg/dL, protein 30 mg/dL) are completely normal and effectively rule out bacterial meningitis. Both parameters fall well within normal ranges and argue strongly against any infectious or inflammatory CNS process.

Interpretation of Your Values

CSF Glucose: 112 mg/dL

  • This is elevated above typical normal ranges (normal CSF glucose typically 40-70 mg/dL in adults)
  • The absolute value must be interpreted in context of serum glucose
  • A CSF glucose >60 mg/dL makes bacterial meningitis extremely unlikely 1
  • Even more definitively, CSF glucose above 2.6 mmol/L (approximately 47 mg/dL) is unlikely to be associated with bacterial meningitis 1

CSF Protein: 30 mg/dL

  • This is normal (typical adult range 15-45 mg/dL)
  • CSF protein <60 mg/dL (0.6 g/L) makes bacterial disease highly unlikely 1
  • In bacterial meningitis, protein is typically >120 mg/dL 2 or averages around 220 mg/dL 3

Clinical Significance

Bacterial meningitis is effectively excluded based on these values. In bacterial meningitis, you would expect:

  • CSF glucose <34 mg/dL 2
  • CSF/plasma glucose ratio <0.36 (sensitivity and specificity of 93%) 1, 4
  • CSF protein >120 mg/dL 2
  • Elevated white blood cell count (typically >2,000 cells/mm³) 3

Important Caveats

The CSF/Plasma Glucose Ratio is Critical

While your absolute CSF glucose is high, you must obtain a simultaneous serum glucose to calculate the CSF/plasma glucose ratio 1, 5. This ratio is more reliable than absolute values:

  • Normal ratio: approximately 0.6-0.67 (two-thirds of plasma glucose) 1
  • Bacterial meningitis: ratio typically <0.36 1, 4

If the patient has significant hyperglycemia (serum glucose >140 mg/dL), the CSF glucose may appear falsely reassuring because glucose transport into CSF becomes saturated 6. However, even in this scenario, your protein level of 30 mg/dL remains strongly reassuring.

Consider Non-Bacterial Causes

With these normal values, if CNS symptoms persist, consider:

  • Viral meningitis/encephalitis - though typically shows some protein elevation
  • Autoimmune encephalitis - may have completely normal CSF early
  • Non-infectious causes of symptoms

Timing Considerations

  • CSF parameters can show diurnal variation, with CSF/blood glucose ratios higher from midnight to 8 AM 7
  • Very early bacterial meningitis (within hours) can occasionally show minimal CSF abnormalities, but this is rare 1

Bottom Line

These values are reassuring and do not support bacterial meningitis or significant CNS infection. The combination of normal-to-elevated CSF glucose and normal protein has extremely high negative predictive value for bacterial disease. If clinical suspicion remains high despite these results, consider viral etiologies or non-infectious causes, but empiric antibacterial therapy is not indicated based on these CSF parameters alone.

References

2
Guideline

practice guidelines for the management of bacterial meningitis.

Clinical Infectious Diseases, 2004

4
Research

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

The American journal of emergency medicine, 2014

6
Research

Cerebrospinal fluid to serum glucose ratio in non-hypoglycorrhachic neurological conditions.

Hong Kong medical journal = Xianggang yi xue za zhi, 2005

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