CSF findings in each type of meningitis bacterial viral and tb meningitis
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I now have comprehensive, authoritative data from multiple major textbooks. Here is the complete, well-structured answer:
CSF Findings in Meningitis: Bacterial vs. Viral vs. TB
Normal CSF (Reference Values)
| Parameter | Normal Value |
|---|---|
| Opening pressure | < 180 mm H₂O |
| WBC count | < 5-10 cells/µL (lymphocytes only) |
| Protein | 15-45 mg/dL |
| Glucose | 50-100 mg/dL |
| CSF/serum glucose ratio | > 0.6 |
Comparative CSF Table
| Parameter | Bacterial | Viral (Aseptic) | TB |
|---|---|---|---|
| Opening pressure | ↑ elevated | Usually normal | ↑ elevated |
| WBC count | 100-5000/µL | 10-300/µL (rarely up to 1000) | 10-300/µL |
| Predominant cell | Neutrophils (PMNs) | Lymphocytes | Lymphocytes (PMNs early in ~25-35%) |
| Protein | 100-500 mg/dL (up to 1000) | 50-100 mg/dL (mild increase) | 100-200 mg/dL (increased) |
| Glucose | < 40 mg/dL (markedly low) | Normal | < 45-50 mg/dL (reduced) |
| CSF/serum glucose ratio | ≤ 0.3 (marked decrease) | Usually normal (> 0.6) | Low (< 0.5) |
| Lactic acid | Mild to marked increase | Normal to mild increase | Mild to moderate increase |
| Gram stain | Positive in 70-80% | Negative | Negative |
| Culture | Positive (bacteria) | Negative (bacteria) | AFB smear/culture (slow, weeks) |
| Key diagnostic test | Gram stain + culture | Virus-specific PCR | AFB smear, culture, PCR for M. tuberculosis |
Key Details Per Type
Bacterial Meningitis
- WBC typically > 1000/µL, predominantly neutrophils
- Glucose < 40 mg/dL (hypoglycorrhachia) is a hallmark
- Protein markedly elevated - can exceed 500 mg/dL
- CSF/serum glucose ratio usually ≤ 0.3
- Gram stain positive in 70-80% of untreated cases
- Common pathogens: S. pneumoniae, N. meningitidis, Listeria, H. influenzae
- Lactic acid: mild to marked increase
Viral (Aseptic) Meningitis
- WBC usually < 100/µL, lymphocytes predominate
- Important caveat: in the first 24-48 hours of enteroviral meningitis, neutrophils may dominate in ~50% of patients - this can mimic bacterial meningitis; repeat LP after 8-12 hours will show shift to lymphocytes
- Glucose is normal (occasionally mildly reduced in herpes, mumps, LCM virus)
- Protein is only mildly elevated (< 150 mg/dL)
- PCR is the diagnostic mainstay (sensitivity 85-100% for enteroviruses)
- Lactic acid: normal to mild increase
TB Meningitis
- WBC 10-300/µL, predominantly lymphocytes (PMNs may dominate in early disease in ~25-35% of patients)
- Glucose reduced to < 45-50 mg/dL - a lymphocytic pleocytosis with low glucose should always raise suspicion for TB or fungal meningitis
- Protein elevated: 100-200 mg/dL
- AFB smear has low sensitivity (< 40%); culture is gold standard but takes weeks
- PCR for M. tuberculosis is faster and more sensitive
- Opening pressure often elevated; may form a characteristic cobweb clot on standing
- Lactic acid: mild to moderate increase
Quick Memory Aid
| Feature | Bacterial | Viral | TB |
|---|---|---|---|
| Cells | PMNs (neutrophils) | Lymphocytes | Lymphocytes |
| Glucose | Very low (< 40) | Normal | Low (< 45) |
| Protein | Very high | Mildly elevated | Elevated |
| Pressure | High | Normal | High |
Key rule: Normal glucose = viral; Low glucose + lymphocytes = TB/fungal; Low glucose + neutrophils = bacterial
Sources: Washington Manual of Medical Therapeutics; Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 598; Neuroanatomy through Clinical Cases, Table 5.7; Goldman-Cecil Medicine; Bradley & Daroff's Neurology in Clinical Practice
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