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Lumbar Puncture
Elevated opening pressure correlates with increased risk of morbidity and mortality in bacterial and fungal meningitis. In bacterial meningitis, elevated opening pressure (reference range is 80-200 mm water) suggests increased ICP from cerebral edema. In viral meningitis, the opening pressure is usually within the reference range. The CSF opening pressure may be elevated at times in cryptococcal meningitis, suggesting increased ICP. The opening CSF pressure is usually elevated in tuberculous meningitis.
The CSF cell count varies depending on the offending pathogen. It is usually in the few hundreds (100-1000 cells/µL) with a predominance of lymphocytes in patients with viral meningitis.
Some cases of echovirus, mumps, and HSV meningitis may produce a neutrophilic picture early in the course of disease.
Go to Lumbar Puncture for complete information on this topic.
See Table 5 "CSF Picture of Meningitis According to Etiologic Agent " and Table 6 "Comparison of CSF Findings by Type of Organism," below.
Table 5. CSF Picture of Meningitis According to Etiologic Agent (Open Table in a new window)
| Agent
| Opening Pressure
| WBC count per µL
| Glucose (mg/dL)
| Protein (mg/dL)
| Microbiology
| | Bacterial meningitis
| 200-300
| 100-5000; >80% PMNs*
| < 40
| >100
| Specific pathogen demonstrated in 60% of Gram stains and 80% of cultures
| | Viral meningitis
| 90-200
| 10-300; lymphocytes
| Normal, reduced in LCM and mumps
| Normal but may be slightly elevated
| Viral isolation, PCR† assays
| | Tuberculous meningitis
| 180-300
| 100-500; lymphocytes
| Reduced, < 40
| Elevated, >100
| Acid-fast bacillus stain, culture, PCR
| | Cryptococcal meningitis
| 180-300
| 10-200; lymphocytes
| Reduced
| 50-200
| India ink, cryptococcal antigen, culture
| | Aseptic meningitis
| 90-200
| 10-300; lymphocytes
| Normal
| Normal but may be slightly elevated
| Negative findings on workup
| | Normal values
| 80-200
| 0-5; lymphocytes
| 50-75
| 15-40
| Negative findings on workup
| | *Polymorphonuclear lymphocytes †Polymerase chain reaction
| Table 6. Comparison of CSF Findings by Type of Organism (Open Table in a new window)
| | Bacterial Meningitis
| Viral Meningitis*
| Fungal Meningitis**
| | Pressure 5-15 cm H2 O
| Increased
| Normal or mildly increased
| Normal or mildly increased in TB. May be increased in fungal. AIDS patients with cryptococcal meningitis have increased risk of blindness, death unless maintained at < 30 cm.
| | Cell count preterm: 0-25 term: 0-22 >6 months: 0-5 mononuclear cells/mm3
| No cell count result can exclude bacterial meningitis. Typically thousands of PMNs, but may be less dramatic or even normal (classically, in very early meningococcal meningitis and in extremely ill neonates). Lymphocytosis with normal CSF chemistries seen in 15-25%, especially when cell counts < 1000 or if partially treated. Approximately 90% of patients with ventriculoperitoneal shunts have CSF WBC count >100 cells/mm3 are infected; CSF glucose usually normal, and organisms are less pathogenic. Cell count and chemistries normalize slowly (over days) with antibiotics.
| Usually < 500 cells, nearly 100% mononuclear. Up to 48 hours, significant PMN pleocytosis may be indistinguishable from early bacterial meningitis; this is particularly true with eastern equine encephalitis. Presence of nontraumatic RBCs in 80% of HSV meningoencephalitis, although 10% have normal CSF results
| Hundreds of mononuclear cells
| | Micro no organisms
| Gram stain 80% sensitive. Inadequate decolorization may mistake H influenzae for gram-positive cocci. Pretreatment with antibiotics may affect stain uptake, causing gram-positive organisms to appear gram negative and decrease culture yield on average 20%.
| No organism
| India ink 80-90% sensitive for fungi; AFB stain 40% sensitive for TB (increase yield by staining supernate from at least 5 cc CSF)
| | Glucose euglycemia: >50% serum hyperglycemia: >30% serum wait 4 h after glucose load
| Decreased
| Normal
| Sometimes decreased. Aside from fulminant bacterial meningitis, the lowest levels of CSF glucose are seen in TB, primary amebic meningoencephalitis, neurocysticercosis
| | Protein preterm: 65-150 term: 20-170 >6 months: 15-45 mg/dL
| Usually >150, may be >1000
| Mildly increased
| Increased; >1000 with relatively benign clinical presentation suggestive of fungal disease
| | *Some bacteria (eg, Mycoplasma, Listeria, Leptospira species, Borrelia burgdorferi [Lyme], spirochetes) produce spinal fluid alterations that resemble the viral profile. An aseptic profile also is typical of partially treated bacterial infections (more than 33% of patients have received antimicrobial treatment, especially children) and the 2 most common causes of encephalitis — the potentially curable HSV and arboviruses. **In contrast, tuberculous meningitis and parasites resemble the fungal profile more closely.
| Take tube #1 to the chemistry lab for glucose and protein. Take tube #2 to the hematology lab for a cell count with differential. Take tube #3 to the microbiology and immunology lab for Gram stain, bacterial culture, acid-fast bacillus (AFB) stain and tuberculosis cultures, India ink stain, cryptococcal antigen testing, and fungal cultures, CIE, VDRL, and cryptococcal antigen, if indicated. Hold tube #4 for a repeat cell count with differential, if needed (or for other subsequent studies not initially ordered).
Research correlates CSF cytokines in children with bacterial meningitis.
According to Seupaul, the following 3 diagnostic tests have clinically useful likelihood ratios for the diagnosis of bacterial meningitis in adults:
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