Cerebrospinal Fluid (CSF) Analysis

Overview

Which investigations are performed on CSF?

Routinely Performed
  • Opening pressure
  • Total Cell count (WBC & RBC)
  • Cell differential count
  • Glucose (CSF/plasma ratio)
  • Total protein
Useful in Specific Situations
  • Microbiological stains:
    • Gram stain
    • Acid-Fast stain
  • Microbiological cultures:
    • Bacterial culture
    • Fungal culture
    • TB culture
  • Microbiological Antigens:
    • VDRL
    • Pneumococcus / meningococcus
    • Cryptococcus
    • Aspergillus
    • Toxoplasmosis
  • Viral PCR
  • Electrophoresis
  • Cytologic examination
  • Specific proteins (CRP, Tau, B-amyloid)

Which samples should be used for tests?

  •  A general consensus is to label sample tubes sequentially from an LP
  • These can then be used for:

1st & 3rd

2nd

4th

  • Cell count & differential
  • Total protein
  • Glucose
  • Other biochemistries
  • Microbiological stains
  • Microbiological cultures

Opening Pressure

What is the normal CSF opening pressure? What can lead to physiological variation?

  • Normal CSF opening pressure 5-20 cm H2O
    • May be up to 25 cm H2O in obese
    • Opening pressure >25 cm H2O diagnostic of intracranial hypertension
  • Meniscus fluctuates:
    • 2-5mm with pulse
    • 4-10mm with respiration
  • Must be measured in the lateral decubitus position:
    • Levels vary with gravity
    • Can be 20-40 cm H20 if measured in the sitting position
  • Opening pressure sure never be lowered by >50%

Appearance

Which conditions can cause abnormal visual appearance of CSF?

Appearance

Clear

Turbid

Yellow / Orange / Pink

Green

Brown

Cause
  • Normal appearance
  • Raised WBC count (>200/mm3)
  • Raised RBC count (>400/mm3)
  • Xanthochromia: subarachnoid haemorrhage, artifactual red cell lysis
  • Hyperbilirubinemia
  • High carotenoids ingestion
  • Rifampicin therapy
  • Hyperbilirubinemia
  • Purulent CSF
  • Meningeal melanomatosis

What is xanthochromia?

  • Xanthochromia is a yellow, orange, or pink discoloration of the CSF
  • Due to the breakdown products of haemoglobin (bilirubin) following lysis of red cells
  • Begins after RBCs have been in CSF for about two hours and can remain for up to 2-4 weeks
  • Ultraviolet light can cause degradation of bilirubin:
    • Can lead to false negatives
    • Samples should be kept in the dark until analysis

Glucose

What is a normal CSF glucose level?

  • A true normal range cannot be given for CSF glucose
  • As a general rule, CSF glucose is 50-66% of serum glucose:
    • Serum glucose must be measured within 2 hours
    • Ratio decreases with increasing serum levels (generally does not go above 16.7 mmol/L regardless of serum levels)

What causes low CSF glucose levels?

  • Can be due to caused due to
    • Utilisation by pathogenic organisms
    • Utilisation by host cells
    • Impaired CSF glucose transport through the blood-brain barrier
  • Conditions where low CSF glucose arises include:
Infective conditions
  • Bacterial infections: low (<40%)
  • Tuberculous infections: very low (<30%)
  • Fungal infections: low-normal
* Normal glucose levels do not rule out infection (up to 50 percent of patients who have bacterial meningitis will have normal CSF glucose)
Perioperative
  • Chemical and inflammatory meningitis
  • Subarachnoid hemorrhage
  • Hypoglycemia

Lactate

Why is CSF lactate measured?

  • Lactate rises in the presence of anaerobic respiration:
    • Mostly arises from host cells even in the presence of infection
    • CSF lactate is independent of blood lactate concentration
  • The relevance of CSF lactate is similar to that of CSF/serum glucose ratio
    • Except for mitochondrial disease, CSF lactate correlates inversely with CSF/serum glucose ratio
    • An increased level can be detected earlier than the reduced glucose concentration

What is normal CSF lactate?

  • The normal value is considered to be <2.8–3.5 mmol/l

What causes an increased CSF lactate?

  • Purulent meningitis (bacterial or fungal)
  • Leptomeningeal metastases
  • Stroke with severe hypoxia
  • Metabolic (mitochondrial) encephalopathy
  • Seizures

Protein

What is a normal CSF protein level?

  • Normal range in an adult is 0.2 – 0.4 g/L
  • May be falsely elevated following a traumatic tap:
    • Can be corrected by subtracting 10mg/L for every 1000 RBCs/mm3
    • Correction is only accurate if the same tube is used for the protein and cell counts.

What are the causes of elevated CSF protein?

Infective conditions

Inflammatory conditions

Vascular conditions

Endocrine conditions

Medications / toxins

Other

  • Bacterial infections
  • Tuberculous infections
  • Fungal infections
  • Cerebral abscess
  • Guillian-Barre Syndrome
  • Multiple sclerosis
  • Subarachnoid haemorrhage
  • Cerebral haemorrhage
  • Cerebral thrombosis
  • Diabetes melitus
  • Hyperthyroidism
  • Hyperadrenalism
  • Phenytoin
  • Ethanol
  • Heavy metals
  • Mechanical obstruction of CSF circulation
  • Traumatic tap
  • Malignancies

Electrophoresis

What is CSF electrophoresis used to detect?

  • Used to assess for oligoclonal bands as a marker of a CNS specific inflammation
  • CSF may contain immunoglobulins from two different sources:
    • Those passively transferred from the plasma during ultrafiltration (Immunoglobulins in the plasma will be mirrored in the CSF)
    • Those synthesized locally within the central nervous system
  • Electrophoresis can be used to detect an antibody clonal response:
    • Paired serum and CSF samples must be analyzed at the same time
    • If an oligoclonal band is present in both samples it suggests systemic infection or inflammation
    • If an oligoclonal band is present in only the CSF sample it suggests a CNS specific condition

What patterns can be seen with paired electrophoresis?

Autoimmune conditions
Multiple sclerosis
Neuro-SLE
Neuro-Behcet's
Neuro-sarcoid
Infective conditions
Acute viral meningoencephalitis (<7 days)
Acute bacterial meningoencephalitis (<7 days)
Subacute sclerosing panencephalitis
Neurosyphilis
Neuro-AIDS
Neuroborreliosis
Neoplastic conditions
Tumours
Hereditary conditions
Ataxia-telangectasia
95%
50%
20%
40%
<5%
<5%
100%
95%
80%
80%
<5%
60%

Cell Count & Differential

What is a normal red cell count in CSF?

  • Normally, there are no RBCs in the cerebrospinal fluid

What are the causes of red cells in the CSF?

  • Traumatic lumbar tap:
    • Occurs in 20% of lumbar punctures
    • Differentiated from haemorrhagic causes by a falling RBC count across three bottles counted in order of collection
  • Subarachnoid haemorrhage
  • Intracerebral haemorrhage
  • Cerebral infarct

What is the normal white cell count in CSF?

  • Normal CSF may contain up to 5 WBCs per mm3 in adults

How can you correct for blood contamination of CSF when determining the white cell count?

  • Blood contaminating CSF in the setting of haemorrhage or traumatic tap can disrupting the white cell count
  • The ratio of WBC to RBC in blood is roughly 1:750
  • It is suggested to correct the white cell count by subtracting 1–2 WBC per 1,000 counted RBC in CSF

What are the causes of raised CSF white cell count  (pleocytosis)?

Infectious conditions
  • Viral meningoencephalitis
  • Bacterial meningoencephalitis
  • TB meningitis
  • Fungal meningitis
  • Neurosyphilis
  • Lyme disease
  • Parasitic infections
  • V-P shunt infection
Inflammatory conditions
  • Cerebral vasculitis
  • Demyelinating disease
Vascular conditions
  • Subarachnoid haemorrhage
  • Subdural haemorrhage
  • Epidural haematoma
  • Stroke
Other
  • Seizures
  • Epidural anaesthesia
  • Cerebral malignancy or metastases

Which cell types predominate in specific neurological conditions?

Neutrophils

Lymphocytes

Plasma cells

‘Mixed reaction’ (neutrophils, lymphocytes and plasma cells)

Eosinophils

Leukaemic Cells

  • Bacterial meningitis
  • Cerebral abscess
  • Seizures
  • CNS haemorrhage
  • Viral meningitis
  • TB meningitis
  • Syphilis
  • Fungal meningitis
  • Parasitic infections
  • Multiple sclerosis
  • TB meningitis
  • TB meningitis
  • Fungal meningitis
  • Chronic bacterial meningitis
  • Parasitic infections
  • V-P shunts (with or without infection)
  • Malignancy
  • Drug reactions
  • Infiltration by haematological malignancy

Microscopy, Culture & PCR

Which microbiological investigations may be carried out on CSF?

  • Staining and microscopic investigation:
    • Gram stain
    • India ink stain (cryptococcus)
    • Acid-fast stain (tuberculosis)
    • Giemsa (toxoplasmosis)
    • Wet preparation (protozoa and helminths)
  • Cultures:
    • Bacterial culture
    • TB culture
    • Fungal culture
  • PCR
  • Serology
  • Antigen detection

How useful is a Gram stain and microscopy in the diagnosis of bacterial CNS infection?

  • Positive in 60-80% of untreated cases of bacterial meningitis:
    • Reduced to 40-60% if partially treated
  • Sensitivity varies according to organism:
    • Up to 90% for pneumococcal or staphylococcal meningitis
    • <50% for listeria meningitis

What is the role of PCR in diagnosing CNS infections?

  • Has a high sensitivity and specificity for viral and certain other infections:
Pathogen
HSV-1
CMV
VZV
EBV
JC virus
Enterovirus
Mycobacterium TB
Specificity (%)
100
75-100
100
100
92-96
100
94-100

What is the role of PCR in diagnosing CNS infections?

Pathogen
Bacterial Infection
Neisseria meningitidis
Streptococcus pneumoniae
Haemophilus influenza
Staphylococcus aureus
Treponema pallidum
Mycobacterium tuberculosis
Listeria monocytogenes
Coxiella burtnetti
Rickettsia
Viral Infection
Herpes simplex virus (HSV)
Varicella zoster virus (VZV)
Enterovirus (echovirus, coxsackie)
Human immunodeficiency virus (HIV)
Epstein Barr virus (EBV)
Cytomegalovirus (CMV
JC virus
Adenovirus
Poliovirus
Rabies virus
Fungal Infection
Aspergillus
Cryptococcus
Parasitic Infection
Toxoplasmosis
Test
Microscopy, culture
Microscopy, culture
Microscopy, culture
Microscopy, culture
Serology
PCR, culture
Microscopy, culture
Serology
Serology
PCR, serology
PCR, serology
PCR, serology
PCR, serology
Serology
Serology
PCR
PCR, culture, antigen detection
PCR
PCR
Antigen detection, culture of biopsy
Antigen detection, microscopy, culture
PCR, serology, biopsy

Normal Composition

What is the normal composition and pressure of cerebrospinal fluid (CSF)?

Opening Pressure (cm/H2O)
Appearance
RBC
(per mm3)
WCC
(per mm3)
Cell Differential
Protein
(g/L)
Oligoclonal Bands
Glucose-Serum Ratio
Lactate
(mmol/L)
Xanthochromia
Normal
5-20
Clear, colourless
<3
<5
Usually lymphocytes and monocytes
0.2-0.4
Absent
0.5-0.66
(2.5-3.5 mmol/L)
<2.8–3.5
Absent

Infective Conditions

What are the characteristic CSF findings in meningitis / encephalitis?

Opening Pressure (cm/H2O)

Appearance

RBC
(per mm3)

WCC
(per mm3)

Cell Differential

Protein
(g/L)

Glucose-Serum Ratio

Lactate
(mmol/L)

Microscopy and Gram Stain

Culture

PCR

Other

Normal
5-20
Clear, colourless
<3
<5
Usually lymphocytes and monocytes
0.2-0.4
0.5-0.66
(2.5-3.5 mmol/L)
<2.8–3.5
-
-
-
-
Bacterial Meningitis
>30
Turbid
Normal
>500
(Up to 100,000)
Neutrophilic (polymorphonuclear) pleocytosis
>1
(High)
<0.4
Elevated
60-80% positive Gram Stain
Up to 80% positive
-
-
Viral Meningitis
Normal or slightly raised
'Gin' Clear
Normal
<100
Lymphocytic (mononucleur) pleocytosis
0.5-1
(Normal-high)
>0.6
Normal
Negative
Viral culture rarely positive (<5%)
HSV, VZV, enterovirus, CMV
-
TB Meningitis
Variable
Fibrin web
Normal
100-500
Lymphocytic (mononucleur) pleocytosis
1.0-5.0
(High-very high)
<0.4
Elevated
Negative
30-50% positive
-
-
Fungal Meningitis
Variable
Fibrin web
Normal
100-500
Lymphocytic (mononucleur) pleocytosis
0.2-5.0
(Variable)
<0.4
Elevated
30% positive acid-fast stain
50-70% positive
-
Cryptococcal Ag

Haemorrhagic Conditions

What are the characteristic CSF findings in subarachnoid haemorrhage (SAH)? How can this be differentiated from a ‘traumatic tap’?

Opening Pressure (cm/H2O)

Appearance

RBC
(per mm3)

WCC
(per mm3)

Protein
(g/L)

Glucose-Serum Ratio

Lactate
(mmol/L)

Other

Normal
5-20
Clear, colourless
<3
<5
0.2-0.4
0.5-0.66
(2.5-3.5 mmol/L)
<2.8–3.5
-
Traumatic Tap
Normal
Grossly bloody or clear
Elevated
Typically varies from tube to tube (greatest in Tube #1)
Elevated
(can correct by subtracting 1 per 1000 RBCs/mm3)
Elevated
(can correct by subtracting 10mg/L for every 1000 RBCs/mm3)
Normal
Normal
Xanthochromia absent
Subarachnoid Haemorrhage
Elevated
Grossly bloody, xanthochromic or clear
Elevated
Elevated
(can correct by subtracting 1 per 1000 RBCs/mm3)
Elevated
(can correct by subtracting 10mg/L for every 1000 RBCs/mm3)
Normal
Normal
Xanthochromia typically present if duration over 2-12 hours

Inflammatory & Malignant Conditions

What are the characteristic CSF findings in inflammatory and malignant conditions?

Opening Pressure (cm/H2O)

Appearance

RBC
(per mm3)

WCC
(per mm3)

Cell Differential

Protein
(g/L)

Oligoclonal Bands

Glucose-Serum Ratio

Lactate
(mmol/L)

Normal
5-20
Clear, colourless
<3
<5
Usually lymphocytes and monocytes
0.2-0.4
Absent
0.5-0.66
(2.5-3.5 mmol/L)
<2.8–3.5
Guillain-Barre Syndrome (GBS)
Normal
Normal
Normal
Normal / Mildly Elevated (<10)
Normal
(Lymphocytic pleocytosis if associated with HIV)
Elevated
(May be normal in first week)
10-20%
Normal
Normal
Multiple Sclerosis (MS)
Normal
Normal
Normal
Normal / Mildly Elevated
Mononuclear
Normal
95%
(highly diagnostic)
Normal
Normal
Multiple Sclerosis (MS)
Normal
Normal
Normal
Normal / Elevated
Malignant cells, mononuclear cells
Elevated
<5%
Normal / Reduced
Unclear

QUESTIONS & OBJECTIVES

  • FRCA Primary
  • FRCA Final
  • FFICM Final

Author

The Guidewire
Trainee in ICM & Anaesthesia

Reviewer

The Guidewire
Trainee in ICM & Anaesthesia