CSF analysis

Parameter	Normal CSF	Bacterial meningitis	Viral meningitis	Tuberculous meningitis	Fungal meningitis
Opening pressure	6–25 cmH₂O	Raised, often >20–30 cmH₂O	Normal or mildly raised	Raised or variable	Often raised, especially cryptococcal
Appearance	Clear	Turbid, cloudy, purulent	Clear	Clear, slightly cloudy Potential fibrin “cobweb” clot	Clear or cloudy
WCC	<5 cells/µL	100–10,000 cells/µL Often >1000	10–1000 cells/µL Usually <250–500	50–1000 cells/µL	20–500 cells/µL May be low/normal if immunocompromised
Predominant cells	Lymphocytes/monocytes	Neutrophils, though lymphocytes may predominate early or after antibiotics	Lymphocytes; neutrophils may predominate early	Lymphocytes; early mixed neutrophils/lymphocytes possible	Lymphocytes; eosinophils possible in some fungi
Protein	0.15–0.45 g/L	>1.0 g/L; often markedly raised	Normal or mildly raised, usually <1.0–1.5 g/L	1.0–5.0 g/L	Raised, often 0.5–2.5 g/L, variable
Glucose	≥2.5 mmol/L or >50–60% serum glucose	Low, often <2.2 mmol/L	Usually normal	Low	Low or normal-low
CSF:serum glucose ratio	~0.6	<0.4	>0.5–0.6	<0.3–0.4	Often <0.5
Microbiology	No organisms	Gram stain, culture, PCR Gram stain sensitivity variable	Viral PCR	AFB stain insensitive; mycobacterial culture, NAAT, Xpert MTB, RIF	Cryptococcal antigen, India ink, fungal culture/PCR

• CSF = cerebrospinal fluid

THINGS TO PUT ON THE FORM

• gram stain
• microscopy
• culture
• xanthochromia
• WCC
• RCC
• protein
• oligoclonal bands
• extended culture
• cryptoccal antigen and Indian ink stain
• ZN stain for acid fast bacilli
• PCR for enterovirus and HSV
• cytology

APPEARANCE

• normally clear
• turbid with infection
• blood stained with SAH and traumatic taps
• yellow with xanthochromia (this takes 6-12 hours to develop after blood enters CSF)

WCC

• normally scant monocytes
• in traumatic tap classically taught to expect 1 WCC : 500 RCC (if normal in peripheral cell counts) but this is not reliable
• polymorphonuclear leukocytosis: bacterial infection
• lymphocytosis: viral, TB, cryptococcal and listerial infections
• mixed lymphocytosis/monocytosis in GBS and status epilepticus

RCC

• increased in traumatic tap and SAH

PROTEIN

• increased in infection: Tb > bacterial > viral
• increased in GBS, vasculitis and sarcoidosis
• oligoclonal bands in multiple sclerosis
• increased in CNS inflammation (including CSF drains and blood in CSF)

GLUCOSE

• normally at least 75% serum glucose
• less than half serum in infections (bacterial, Tb and fungal infections) and vasculitis and sarcoidosis

OTHER FINDINGS

• xanthochromic index with spectrophotometry (in SAH)
• extended culture (Listeria, Cryptococcus)
• India Ink stain for cryptococcus
• ZN stain for acid fast bacilli
• PCR for enterovirus and HSV
• cytology

Meningitis

• Infective
  • Bacterial
  • Aseptic – Viral, TB, Fungi, Parasites
• Non-infective
  • Malignancy
  • Auto-immune

Age-related Causes of Meningitis

• Bacterial:
  • Neonatal (<3/12)
    • Gram negative (E coli)(Pseudomonas), Listeria, Group B strep, Coag –ve staphylococcus
  • 3/12 to 15 years
    • Neiserria meningitidis, Pneumococcus (strep pneumonia), Haemophilus pneumonia
  • Adult > 15 years
    • N meningitidis, s. pneumonia, listeria, klebsiella, s. aureus
  • Elderly
    • Gram negatives predominate
  • Immunocompromised
    • Complement deficiency – Neiserria
    • Humoral or asplenic – Neiserria, enterovirus
    • Sickle cell disease – Capsulated organisms
• Aseptic meningitis (Generally accepted as mainly viral meningitis)
  • Lymphocytosis, variable protein elevation and normal glucose
  • Viral
    • Echovirus, Enterovirus, Mumps
    • HSV 1 + 2, CMV, VZV, EBV
  • Other
    • TB, Nocardia, Leptospira, Treponema
    • Fungi, rickettsia, parasites
    • Malignancy, auto-immune

Specific Risk Factors

• Pneumococcus: (40%) – Otitis media, head injury, pneumonia, immunocompromised
• N meningitidis: (30%) – Children and adolescents
• Staphylococcus: Penetrating skull injury, ear or neuro operations
• Fungal: HIV and organ transplant
• Listeria: Extremes of age
• H Influenzae: (3%)  – Head trauma with CSF leak, otitis, sinusitis, anatomical defects such as dermal sinus tracts
• Anaerobes: Consider brain abscess, elderly

References and Links