CSF Findings in Bacterial vs. Viral Meningitis

Understanding the cerebrospinal fluid (CSF) findings in meningitis is essential for nurses and nursing students. CSF analysis, usually obtained through a lumbar puncture, helps differentiate bacterial meningitis from viral meningitis.

Opening Pressure

The first measurement during a lumbar puncture is the opening pressure:

• Normal: 5–15 mmHg
• Bacterial meningitis: Usually elevated
• Viral meningitis: Typically normal

Appearance of CSF

The visual appearance of CSF provides important diagnostic clues:

• Bacterial meningitis: Cloudy due to neutrophils, protein, and bacterial debris
• Viral meningitis: Clear, as there is less cellular debris

Glucose Levels

Glucose concentration in CSF differs between bacterial and viral infections:

• Bacterial meningitis: Low glucose (<40 mg/dL) because bacteria consume glucose
• Viral meningitis: Normal glucose

White Blood Cell Count (WBC)

WBC counts indicate the type of immune response:

• Bacterial meningitis: Very high WBC count, predominantly neutrophils
• Viral meningitis: Elevated WBC count, predominantly lymphocytes

Protein Levels

Protein levels rise due to inflammation and vascular changes:

• Bacterial meningitis: High protein from neutrophil influx and increased vascular permeability
• Viral meningitis: Slightly elevated protein

Culture Results

CSF cultures confirm the type of infection:

• Bacterial meningitis: Cultures positive, helping identify the pathogen
• Viral meningitis: Cultures negative

Cheatsheet to Help You Remember

Key Takeaways for Nursing Students

• Bacterial meningitis: High opening pressure, cloudy CSF, low glucose, high neutrophils, high protein, positive culture
• Viral meningitis: Normal opening pressure, clear CSF, normal glucose, high lymphocytes, slightly elevated protein, negative culture

You may be interested in: Meningitis Nursing Review

_References:

_{Centers for Disease Control and Prevention. (2025, September 9). About bacterial meningitis. Centers for Disease Control and Prevention. https://www.cdc.gov/meningitis/about/bacterial-meningitis.html}

_{Centers for Disease Control and Prevention. (2025, September 9). About viral meningitis. https://www.cdc.gov/meningitis/about/viral-meningitis.html}