• FUNDAMENTALS & INVESTIGATIONS
  • COMMON CONDITIONS

Expand All
Close All

Tests & Samples

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
  • Viral culture
  • Lactate
  • Electrophoresis
  • Cytologic examination
  • Specific proteins (CRP, Tau, B-amyloid)

Which samples should be collected for analysis and how much CSF is required?

  • A general consensus is to label sample tubes sequentially from an LP
  • These can then be used for:
1st
  • Minimum 3 drops
  • More as able up to 0.5ml*
  • Total protein
  • Glucose
  • Other biochemistries
2nd & 3rd
  • Minimum 3 drops (6 for cryptococcus)
  • More as able up to 2.5ml*
  • Cell count & differential
  • Microbiological stains
  • Microbiological cultures•
4th
  • 20 Drops
  • 1ml*
  • Xanthochromia (Protect this sample from the light by placing it in a thick brown envelope outside the usual plastic specimen bag)
  • *1mL is about 20 drops from the Luer connector on a needle
  • A serum sample must be sent simultaneously for glucose and oligoclonal bands
McIntryre (2007)

L

UK Immunochemistry Working Group

D

What are the considerations for commonly performed CSF investigations?

Routinely Performed
Volume
Laboratory
Considerations
Microbiology (Bacteriology, TB, cryptococcus)
>3 drops (6 drops for cryptococcus) but as much as is practically possible
Microbiology
  • Increased sensitivity with higher volumes of CSF
Viral PCR & Culture
>4 drops but as much as is practically possible
Virology
  • Increased sensitivity with higher volumes of CSF
Biochemistry
>3 drops but more if practically possible
Biochemistry
  • Send paired serum protein and glucose samples
Xanthochromia
20 drops
Biochemistry
  • Transport in opaque envelope or wrap sample container in foil.
Oligoclonal Bands
20 drops
Immunology
  • Send paired serum serology sample
Cytology
50 drops or as much as is practically possible
Neuropathology
  • Ensure swift transport to laboratory
Lactate
20 drops
Biochemistry
  • Send paired serum lactate sample

McIntryre (2007)

L

UK Immunochemistry Working Group

D

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
Cause
Clear
  • Normal appearance
Turbid
  • Raised WBC count (>200/mm3)
  • Raised RBC count (>400/mm3)
Yellow / Orange / Pink
  • Xanthochromia: subarachnoid haemorrhage, artifactual red cell lysis
  • Hyperbilirubinemia
  • High carotenoids ingestion
  • Rifampicin therapy
Green
  • Hyperbilirubinemia
  • Purulent CSF
Brown
  • 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
  • Bacterial infections
  • Tuberculous infections
  • Fungal infections
  • Cerebral abscess
Inflammatory conditions
  • Guillian-Barre Syndrome
  • Multiple sclerosis
Vascular conditions
  • Subarachnoid haemorrhage
  • Cerebral haemorrhage
  • Cerebral thrombosis
Endocrine conditions
  • Diabetes melitus
  • Hyperthyroidism
  • Hyperadrenalism
Medications / toxins
  • Phenytoin
  • Ethanol
  • Heavy metals
Other
  • 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

In which conditions are abnormal CSF oligoclonal bands identified with paired electrophoresis?

Autoimmune conditions
Autoimmune conditions
Multiple sclerosis
95%
Neuro-SLE
50%
Neuro-Behcet's
20%
Neuro-sarcoid
40%
Infective conditions
Infective conditions
Acute viral meningoencephalitis (<7 days)
<5%
Acute bacterial meningoencephalitis (<7 days)
<5%
Subacute sclerosing panencephalitis
100%
Neurosyphilis
95%
Neuro-AIDS
80%
Neuroborreliosis
80%
Neoplastic conditions
Neoplastic conditions
Tumours
<5%
Hereditary conditions
Hereditary conditions
Ataxia-telangectasia
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
  • Bacterial meningitis
  • Cerebral abscess
  • Seizures
  • CNS haemorrhage
Lymphocytes
  • Viral meningitis
  • TB meningitis
  • Syphilis
  • Fungal meningitis
  • Parasitic infections
  • Multiple sclerosis
Plasma cells
  • TB meningitis
‘Mixed reaction’ (neutrophils, lymphocytes and plasma cells)
  • TB meningitis
  • Fungal meningitis
  • Chronic bacterial meningitis
Eosinophils
  • Parasitic infections
  • V-P shunts (with or without infection)
  • Malignancy
  • Drug reactions
Leukaemic Cells
  • 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
Specificity (%)
HSV-1
100
CMV
75-100
VZV
100
EBV
100
JC virus
92-96
Enterovirus
100
Mycobacterium TB
94-100

What is the role of PCR in diagnosing CNS infections?

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

Normal Composition

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

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

Infective Conditions

What are the characteristic CSF findings in meningitis / encephalitis?

Normal
Bacterial Meningitis
Viral Meningitis
TB Meningitis
Fungal Meningitis
Opening Pressure (cm/H2O)
5-20
>30
Normal or slightly raised
Variable
Variable
Appearance
Clear, colourless
Turbid
'Gin' Clear
Fibrin web
Fibrin web
RBC
(per mm3)
<3
Normal
Normal
Normal
Normal
WCC
(per mm3)
<5
>500
(Up to 100,000)
<100
100-500
100-500
Cell Differential
Usually lymphocytes and monocytes
Neutrophilic (polymorphonuclear) pleocytosis
Lymphocytic (mononucleur) pleocytosis
Lymphocytic (mononucleur) pleocytosis
Lymphocytic (mononucleur) pleocytosis
Protein
(g/L)
0.2-0.4
>1
(High)
0.5-1
(Normal-high)
1.0-5.0
(High-very high)
0.2-5.0
(Variable)
Glucose-Serum Ratio
0.5-0.66
(2.5-3.5 mmol/L)
<0.4
>0.6
<0.4
<0.4
Lactate
(mmol/L)
<2.8–3.5
Elevated
Normal
Elevated
Elevated
Microscopy and Gram Stain
-
60-80% positive Gram Stain
Negative
Negative
30% positive acid-fast stain
Culture
-
Up to 80% positive
Viral culture rarely positive (<5%)
30-50% positive
50-70% positive
PCR
-
-
HSV, VZV, enterovirus, CMV
-
-
Other
-
-
-
-
Cryptococcal Ag

Haemorrhagic Conditions

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

Normal
Traumatic Tap
Subarachnoid Haemorrhage
Opening Pressure (cm/H2O)
5-20
Normal
Elevated
Appearance
Clear, colourless
Grossly bloody or clear
Grossly bloody, xanthochromic or clear
RBC
(per mm3)
<3
Elevated
Typically varies from tube to tube (greatest in Tube #1)
Elevated
WCC
(per mm3)
<5
Elevated
(can correct by subtracting 1 per 1000 RBCs/mm3)
Elevated
(can correct by subtracting 1 per 1000 RBCs/mm3)
Protein
(g/L)
0.2-0.4
Elevated
(can correct by subtracting 10mg/L for every 1000 RBCs/mm3)
Elevated
(can correct by subtracting 10mg/L for every 1000 RBCs/mm3)
Glucose-Serum Ratio
0.5-0.66
(2.5-3.5 mmol/L)
Normal
Normal
Lactate
(mmol/L)
<2.8–3.5
Normal
Normal
Other
-
Xanthochromia absent
Xanthochromia typically present if duration over 2-12 hours

Inflammatory & Malignant Conditions

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

Normal
Guillain-Barre Syndrome (GBS)
Multiple Sclerosis (MS)
Metastases
Opening Pressure (cm/H2O)
5-20
Normal
Normal
Normal
Appearance
Clear, colourless
Normal
Normal
Normal
RBC
(per mm3)
<3
Normal
Normal
Normal
WCC
(per mm3)
<5
Normal / Mildly Elevated (<10)
Normal / Mildly Elevated
Normal / Elevated
Cell Differential
Usually lymphocytes and monocytes
Normal
(Lymphocytic pleocytosis if associated with HIV)
Mononuclear
Malignant cells, mononuclear cells
Protein
(g/L)
0.2-0.4
Elevated
(May be normal in first week)
Normal
Elevated
Oligoclonal Bands
Absent
10-20%
95%
(highly diagnostic)
<5%
Glucose-Serum Ratio
0.5-0.66
(2.5-3.5 mmol/L)
Normal
Normal
Normal / Reduced
Lactate
(mmol/L)
<2.8–3.5
Normal
Normal
Unclear
Return to Top

Author

The Guidewire
Trainee in ICM & Anaesthesia

Reviewer

The Guidewire
Trainee in ICM & Anaesthesia

Related Pages: