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This guide provides a structured approach to cerebrospinal fluid (CSF) interpretation, including typical CSF results for specific disease processes. Reference ranges vary between labs, so always consult your local medical school or hospital guidelines.

Normal CSF ranges (adults)

Appearance: Clear and colourless

White blood cells (WBC): 0 – 5 cells/µL

  • No neutrophils present, primarily lymphocytes
  • Normal cell counts do not rule out meningitis or any other pathology

Red blood cells (RBC): 0 – 10/mm³

Protein: 0.15 – 0.45 g/L (or <1% of the serum protein concentration)

Glucose: 2.8 – 4.2 mmol/L (or ≥ 60% plasma glucose concentration)

Opening pressure: 10 – 20 cm H2O

CSF findings in specific diseases

Bacterial meningitis

Appearance: Cloudy and turbid

Opening pressure: Elevated (>25 cm HO)

WBC: Elevated >100 cell/µL (primarily polymorphonuclear leukocytes (>90%))

Glucose level: Low (<40% of serum glucose)

Protein level: Elevated (>50 mg/dL)

 

Causes:

  • Newborns: Listeria monocytogenes, E. Coli, Group B Streptococci
  • Older children: Neisseria meningitidis, Haemophilus influenzae Type B, Streptococcus pneumoniae
  • Adults: Neisseria meningitidis, Streptococcus pneumoniae, Listeria monocytogenes

 

Symptoms:

  • Headache
  • Fever
  • Neck stiffness
  • Photophobia
  • Meningococcal meningitis presents with a characteristic petechial rash

 

Further investigations:

  • CSF gram stain and cultures
  • CSF bacterial antigens
  • CSF PCR
  • Blood cultures
  • Imaging to rule out other intracranial pathology – CT / MRI head

 

Viral (aseptic) meningitis

Appearance: Clear

Opening pressure: Normal or elevated

WBC: Elevated (50 – 1000 cells/µL, primarily lymphocytes, can be PMN early on)

Glucose level: Normal (>60% serum glucose however may be low in HSV infection)

Protein level: Elevated (>50 mg/dL)

 

Causes:

  • Herpes simplex virus (HSV 2 is more common than HSV 1)
  • Enteroviruses
  • Varicella zoster virus (VZV)
  • Mumps
  • HIV
  • Adenovirus

 

Symptoms:

  • Headache
  • Fever
  • Neck stiffness
  • Photophobia

 

Further investigations:

  • CSF PCR for viruses (e.g. Herpes simplex virus (HSV) / Varicella-zoster virus (VZV))
  • Blood cultures
  • Imaging to rule out other intracranial pathology – CT / MRI head

 

Fungal meningitis

Appearance: Clear or cloudy

Opening pressure: Elevated

WBC: Elevated (10 – 500 cells/µL)

Glucose level: Low

Protein level: Elevated

 

Causes:

  • Cryptococcus neoformans
  • Candida

 

Symptoms:

  • Patients are often immunocompromised
  • Headache
  • Confusion
  • Nausea
  • Vomiting
  • Fever and neck stiffness are less common

 

Further investigations:

  • CSF cultures
  • CSF PCR
  • CSF staining
  • HIV test (with consent)
  • Blood cultures
  • Imaging to rule out other intracranial pathology – CT / MRI head

 

Tuberculosis meningitis

Appearance: Opaque, if left to settle it forms a fibrin web

Opening pressure: Elevated

WBC: Elevated (10 – 1000 cells/µL, Early PMNs then mononuclears)

Glucose level: Low

Protein level: Elevated (1-5 g/L)

 

 

Symptoms:

  • Headache
  • Fever
  • Neck stiffness
  • Photophobia
  • Delirium
  • Cranial nerve palsies

 

Further investigations:

  • CSF cultures
  • CSF bacterial antigens
  • CSF PCR
  • HIV test (with consent)
  • Blood cultures
  • Imaging to rule out other intracranial pathology – CT / MRI head
  • Chest X-ray

 

Subarachnoid haemorrhage

Appearance: Blood stained initially, then xanthochromia (yellowish) >12 hours later

Opening pressure: Elevated

WBC: Elevated (WBC to RBC ratio of approx 1:1000)

RBC: Elevated

Glucose level: Normal

Protein level: Elevated

 

Causes:

  • Trauma
  • Vascular malformations (e.g. aneurysms, arteriovenous malformations)

 

Symptoms:

  • Sudden onset “thunderclap” headache (patients may describe it as the “worst headache ever”)
  • Stiff neck
  • Vomiting
  • Seizures
  • Confusion
  • Neurological deficits (e.g. weakness / sensory disturbance)

 

Further investigations:

  • Cerebral angiogram
  • CT angiography

 

Guillain Barre syndrome

Appearance: Clear or xanthochromia

Opening pressure: Normal or elevated

WBC: Normal

Glucose level: Normal

Protein level: Elevated (>5.5 g/L)

 

Causes:

  • Campylobacter jejuni
  • CMV
  • EBV
  • Mycoplasma pneumonia
  • VZV

 

Symptoms:

  • Often occurs after a recent bacterial / viral illness
  • Symmetrical ascending muscle weakness primarily affecting proximal musculature (trunk/respiratory muscles)

 

Further investigations:

  • Serologic studies
  • Nerve conduction studies
  • EMG
  • Imaging to rule out other intracranial pathology – CT / MRI head

 

Multiple sclerosis

Appearance: Clear

Opening pressure: Normal

WBC: 0 – 20 cells/µL (primarily lymphocytes)

Glucose level: Normal

Protein level: Mildly elevated (0.45 – 0.75 g/L)

 

Symptoms:

  • Optic neuritis
  • Limb weakness
  • Sensory disturbances
  • Diplopia
  • Ataxia

 

Further investigations:

  • MRI head
  • Oligoclonal bands of IgG on electrophoresis (CSF and Serum)
  • Evoked potential tests (visual/somatosensory)

Worked examples

Case 1

A 55-year-old woman has been getting more confused over the last 2 months. Over the last 3 days, she has been vomiting and suffering from lack of energy. She has no neck stiffness and a CD4 count of 100/mm³

CSF results

Appearance: Cloudy

Opening pressure: 25 cm HO

WBC: 400 cells/µL

Glucose level: < 40% of serum glucose concentration

Protein level: 1g/L

Reveal answer

This is fungal meningitis, in this particular case this lady is found to have cryptococcal meningitis on CSF culture. The patient is also found to have HIV, likely the cause of her impaired immune function (CD4 count 100/mm³), leaving her vulnerable to cryptococcal infection.

 

Case 2

A 28 year old male presents with a 12 hour history of high fever, severe headache, confusion, photophobia and neck stiffness. He has no significant past medical history and takes no regular medication.

 

CSF results

Appearance: Cloudy

Opening pressure: 30 cm HO

WBC: 936 cells/µL (>95% PMN cells)

Glucose level: < 40% of serum glucose

Protein level: 3 g/L

Reveal answer

This is bacterial meningitis. This young gentleman has presented with meningeal symptoms, fever, confusion which have progressed rapidly over the last 12 hours. The CSF is cloudy on inspection, the white cell count is significantly raised and glucose levels are low. The history and CSF results are strongly suggestive of bacterial meningitis and therefore he should be treated empirically whilst culture results are awaited.

Case 3

A 38 year old female presents with 24 hours of headache, photophobia, mild neck stiffness, in addition to coryzal symptoms. She is fully orientated and her observations are stable.

 

CSF results

Appearance: Clear

Opening pressure: 23 cm HO

WBC: 150 cells /µL (primarily lymphocytes)

Glucose level: Normal

Protein level: 90 mg/dL

 

Reveal answer

This is viral meningitis.  This lady has presented with a history of meningitic symptoms alongside coryzal symptoms which suggests the presence of a viral type illness. The CSF findings are more suggestive of viral meningitis given the clear appearance of the CSF, the mildly raised WCC (consisting mainly of lymphocytes), raised protein level and normal glucose. Further investigations including CSF PCR can be useful in identifying the specific virus.

 

Case 4

A 52 year old male presents to A&E with history of a sudden onset severe headache which occurred whilst he was at his desk yesterday. Since the headache he has been feeling nauseated, but he is otherwise well and fully orientated. Examination is largely unremarkable, but he does appear to have some mild neck stiffness.

 

CSF results

Appearance: Yellowish

Opening pressure: 23 cm HO

WBC: Normal

Red cell count: Raised

Glucose level: Normal

Protein level: 80 mg/dL

Xanthochromia: positive

Reveal answer

This is subarachnoid haemorrhage (SAH). The typical history of a sudden severe headache (often described as thunderclap) and meningitic symptoms (neck stiffness) is strongly suggestive of SAH. CT head is often the first line investigation, but it has a sensitivity of 98% in the first 12 hours and becomes less sensitive after that. As a result lumbar puncture is used to rule out SAH. The CSF typically shows a persistently raised red cell count (due to blood present in the CSF from the initial bleed). Within several hours, the red blood cells in the cerebrospinal fluid are destroyed, releasing their oxygen-carrying molecule heme, which is metabolized by enzymes to bilirubin, a yellow pigment. This yellow pigment can be detected and it’s presence is referred to as xanthochromia

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