Which cerebrospinal fluid (CSF) finding is most characteristic of bacterial meningitis compared to viral meningitis?

Explanation

## CSF Profile in Bacterial vs Viral Meningitis **Key Point:** Bacterial meningitis characteristically presents with neutrophilic pleocytosis (>80% neutrophils), markedly elevated protein (>100 mg/dL), and **low CSF glucose** (typically <40 mg/dL or CSF:serum glucose ratio <0.4). This triad is pathognomonic for bacterial meningitis. **High-Yield:** The low glucose in bacterial meningitis occurs because bacteria consume glucose and impair glucose transport across the blood-brain barrier via inflammatory mediators. ### Comparison Table | Feature | Bacterial | Viral | Fungal | | --- | --- | --- | --- | | **Cell type** | Neutrophils (>80%) | Lymphocytes (>50%) | Lymphocytes | | **Glucose** | Low (<40 mg/dL) | Normal (>40 mg/dL) | Low | | **Protein** | Very high (>100 mg/dL) | Mildly elevated (50–100 mg/dL) | Markedly elevated (>100 mg/dL) | | **Gram stain** | Often positive | Negative | Negative | **Clinical Pearl:** The combination of **low CSF glucose + high protein + neutrophilic pleocytosis** should trigger immediate empiric antibiotics (ceftriaxone + vancomycin ± ampicillin) without waiting for culture confirmation. **Mnemonic — BacMen (Bacterial Meningitis):** **B**acteria consume glucose → **Low glucose**, **N**eutrophils predominate, **P**rotein markedly elevated.