CSF: Chemistry and
Dr. Nilesh Chandra
Objectives of the discussion:
• CSF production and circulation
• Normal CSF values and pressures
• Functions of CSF
• CSF Analysis- Biochemical, Microbiological and
Pathological, including disease markers
• Precautions and Contraindications to CSF
• First report of existence of CSF – 17th century B.C.
• Hippocrates – 4th B.C.
• Galen discovered ventricular cavities – 2 A.D.
• Vesalius – watery humour – 16th centuryA.D.
• Magendie performed first tap of CSF in 1825.
Cerebrospinal Fluid (CSF):
•Liquor cerebrospinalis: clear, colorless fluid
•occupies the subarachnoid space and the
ventricular system around and inside the
brain and spinal cord.
•It acts as a "cushion" or buffer for the
cortex, providing a basic mechanical and
immunological protection to the brain inside
•It is produced in the choroid plexus.
Intracranial volumetric distribution of cerebrospinal fluid,
blood, and brain parenchyma
•The CSF is produced at a rate of 500 ml/day.
•The brain can contain only 135 to 150 ml
•The CSF turn over is about 3.7 times a day.
Nervous System Compartment Volume of CSF (ml)
Cranial Subarachnoid Space 100
Spinal subarachnoid Space 25
Lateral Ventricular Horns 25-30
Third Ventricle 2-3
Fourth Ventricle 2-3
Volumetric distribution of cerebrospinal
•Produced by modified ependymal cells
(approx. 50-70%), remainder is formed
around blood vessels, & along ventricular
•Circulates from the lateral ventricles to the
Interventricular foramen, Third ventricle,
Cerebral aqueduct, Fourth ventricle, Median
aperture and Lateral apertures, Subarachnoid
space over brain and spinal cord.
•CSF is reabsorbed into venous sinus blood
via arachnoid granulations.
•CSF pressure, as measured by lumbar puncture (LP), is
10-18 cmH2O (with the patient lying on the side)
•20-30cmH2O with the patient sitting up.
•In newborns, CSF pressure ranges from 8 to 10 cmH2O.
•When lying down, CSF pressure as estimated by lumbar
puncture is similar to the intracranial pressure.
•There are quantitative differences in the distributions of
a number of proteins in the CSF.
CSF serves four primary purposes:
•Buoyancy: The actual mass of human brain: 1400 g; net
weight of the brain suspended in CSF: 25 g
•Protection: CSF protects the brain tissue from injury when
jolted or hit.
•Chemical stability: CSF flows throughout the inner
ventricular system in the brain, is absorbed back into the
bloodstream, rinsing the metabolic waste from the central
nervous system through the blood-brain barrier.
•Prevention of brain ischemia
Normal Values for Adults (Lumbar CSF)
Opening pressure 50–200 mm H2O CSF (range in literature)
Turbidity Crystal clear
Mononuclear cells <5 per mm
Polymorphonuclear leukocytes 0
Total protein 22–38 mg/dl (mean from literature)
Range 9–58 mg/dl (mean ± 2.0 SD
Glucose 60–80% of blood glucose
Reference ranges for CSF constituents
Substance Lower limit Upper limit Unit
to % of that in
RBCs n/a 0/ negative
WBCs 0 3
pH 7.28 7.32 (unitless)
44 50 mmHg
5.9 6.7 kPa
40 44 mmHg
5.3 5.9 kPa
Chloride 115 130[ mmol/L >100%
50 80 mg/dL
2.2, 2.8 3.9, 4.4 mmol/L
Protein 15 40, 45 mg/dL ~1%
Reference ranges for ions and other
molecules in CSF
Substance Lower limit Upper limit Unit
to % of that in
Osmolality 280 300 mmol/L
Sodium 135 150 mmol/L
Potassium 2.6[ 3.0 mmol/L
Calcium 1.00 1.40 mmol/L ~50%
Creatinine 50 110 µmol/L
Phosphorus 0.4 0.6 µmol/L
Urea 3.0 6.5 mmol/L
Blood Brain Barrier
• Brain capillaries show no fenestrations or pinocytotic (transportation)
vesicles and have tight junctions that almost fuse adjacent cells. This
anatomy creates the blood-brain barrier (BBB).
• The BBB separates plasma from the interstitial space of the CNS and
affects in a critical fashion the traffic of molecules in and out of the
• Lipophilic compounds cross the BBB easier than hydrophilic ones do;
small lipophilic molecules diffuse freely.
• Some hydrophilic compounds enter the brain with the help of
transporters;larger molecules enter via receptor-mediated endocytosis.
• The BBB protects the brain from toxic substances but impedes also the
entry of drugs.
• Hypertonic stimuli and chemical substances including glutamate and
certain cytokines can open the BBB.
• HIE and inflammatory mediators produced in sepsis disrupt the BBB.
• The normal CSF is crystal clear.
• The occurrence of pleocytosis: usual reason for cloudy fluid.
• 200 white cells/cmm can be present without altering clarity.
• Over 500 white cells/cmm usually produces cloudiness.
• Red cell concentrations between 500 and 6000 per cmm can
cause the fluid to appear cloudy, while concentrations of over
6000 give a grossly bloody appearance.
• A markedly elevated protein can also alter the clarity
• The clarity of the fluid is of little clinical use, except to provide
an immediate indication of abnormality of the CSF. A very
useful point to remember is that a large number of cells can
be present without affecting the clarity.
Analysis of Xanthochromic CSF
Technique Compare CSF with a similar volume of water in
an identical tube; look down the longitudinal
axis of the tube, against a white background;
ask the ward clerk to see if there is any
difference in the two tubes.
Pigments seen in subarachnoid hemorrhage (SAH)
Oxyhemoglobin Pink or orange color; released into CSF in 2 hours
after SAH, due to RBC lysis; may be released
within 30 minutes if RBC greater than
; maximum color in 36 hours,
disappears in 7 to 10 days; cerebrospinal fluid
must be examined immediately after the LP,
since oxyhemoglobin can be produced by lysis of
RBC in the test tube.
Bilirubin Produces the yellow pigment, or xanthochromia
of CSF; produced in vivo by the conversion of
free hemoglobin by macrophages and other
leptomeningeal cells; not seen for 10 to 12 hours
after the hemorrhage; reaches a maximum in 48
hours, and persists 2 to 4 hours.
Other causes of xanthochromia
Protein Protein over 150 mg/dl produces xanthochroma, the intensity paralleling the amount of
RBCs RBC over 100,000/mm
produce xanthochromia as a result of serum brought with them
Jaundice Serum bilirubin of 15 mg/dl produces xanthochromia; lower levels will do so when
elevated protein is present; the level of serum bilirubin that produces xanthochromia
appears to be quite variable
Carotene Hypercarotenemia in food faddists produces xanthochromia
Others Subdural hematomas, trauma, and clots in other locations will produce xanthochromia
WBCs The WBC/RBC ratio is similar to that of the plasma in traumatic taps and fresh SAH; a
few days old SAHwill produce a chemical meningitis, elevating the number of WBC.
Glucose CSF glucose can be decreased (10 to 50 mg/dl) in SAH present 4 to 7 days
Protein Each 1000 RBC min raises CSF protein 1.5 mg/dl
Tubes 1 to 3 show decreasing RBC; supernate is colorless if it is examined within 30
minutes, provided the conditions listed above are not present; on rare occasions
patients with SAH have decreased cells from tubes 1 to 3, perhaps due to layering of
blood in a recumbent patient; the color of the supernate should provide the answer in
this rare event; if there is any doubt, immediately do another lumbar puncture in a
different interspace; abnormal CSF from a traumatic tap can persist at least 5 days, and
• CSF proteins are derived from serum proteins with the exception of
the trace proteins and some beta globulins.
• Serum proteins enter the CSF by means of pinocytosis.
• Clinical usefulness of CSF proteins is presently limited to the
measurement and characterization of total protein and IgG.
• 3 pathological conditions cause abnormalities of the CSF proteins:
– Increased entry of plasma proteins due to increased
permeability of the blood–brain barrier.
– Local synthesis of proteins within the central nervous system.
Clinical interest is limited to IgG currently.
– Impaired resorption of CSF proteins by the arachnoid villi.
• Elevated CSF total protein is highly suggestive of neurologic disease.
• Total protein over 500 mg/dl is seen in meningitis, cord tumor with
spinal block, and bloody CSF.
• Each 1000 RBC/mm3 raises the CSF protein 1.5 mg/dl.
IgG in CSF:
• IgG concentration in the CSF is normally 4.6 ± 1.9 mg/dl.
• It is the principal immunoglobulin in the CSF.
• Local synthesis within the central nervous system occurs in a variety of
inflammatory disorders: multiple sclerosis, neurosyphilis, subacute sclerosing
panencephalitis, progressive rubella encephalitis, viral
meningoencephalitides, sarcoidosis, etc.
• IgG can be characterized by agar gel electrophoresis and isoelectric focusing
for the identification of oligoclonal banding in addition to quantification. Up to
90% of cases of confirmed multiple sclerosis have elevated gamma globulin
and/or oligoclonal bands. Oligoclonal bands represent a qualitative change in
• The appearance of oligoclonal bands in the CSF in the absence of similar
bands in the serum is an indication of gamma globulin production in the
central nervous system even when quantified levels of gamma globulin are
• The difficulty in assessing IgG levels in the CSF lies in distinguishing whether
elevated levels are due to increased permeability of the blood–brain barrier,
or whether there is local synthesis in the central nervous system.
Fractionation of CSF Protein
Mechanism of elevated
CSF protein CSF/serum albumin ratio CSF/serum IgG ratio CSF IgG/albumin index
Obstruction to CSF
Elevated Elevated Normal
Elevated Elevated Normal
Increased CNS protein
Normal Elevated Elevated
Cerebrospinal fluid (CSF) protein is increased by increased permeability of the blood–CSF barrier or
increased CNS protein synthesis. Concurrent measurement of albumin and IgG in both CSF and serum by
immunochemical methods is useful in distinguishing these two mechanisms. Since albumin is neither
synthesized nor metabolized intrathecally, increased CSF albumin relative to serum albumin reflects loss of
functional integrity of the blood–CSF barrier. Synthesis of immunoglobin does occur in the CNS; therefore,
increased CSF IgG relative to serum reflects either permeability changes or increased CNS synthesis.
Comparing the CSF/serum IgG and CSF serum albumin ratios provides a specific index of local immunoglobin
synthesis since the IgG ratio is corrected for permeability changes.
Local synthesis of IgG occurs in demyelinating and some chronic inflammatory CNS diseases. IgG produced
within the CNS tends to have restricted heterogeneity and can be detected as oligoclonal banding on agar
gel protein electrophoresis. Oligoclonal banding occurs in the same spectrum of diseases as elevated CSF
IgG/albumin index; however, electrophoretic detection is considered a more sensitive marker for multiple
• The usual CSF glucose is 60 to 80% of the plasma glucose.
• Glucose is utilized for energy by cellular elements close to the
CSF; this is the principal means of glucose removal.
• The most common cause of lowered CSF glucose
(hypoglycorrhachia) is meningitis: bacterial, tuberculous, fungal,
amebic, acute syphilitic, chemical, and certain of the viral
meningitides (mumps, herpes simplex, and herpes zoster).
• Lowered CSF glucose occurs in about 15% of SAH, reaching a
nadir 4 to 8 days after the bleed.
• Meningeal carcinomatosis also produces hypoglycorrhachia. A
large variety of tumors have been implicated. Cytologic
examination of the fluid is often the key to diagnosis.
• Other causes of lowered CSF glucose include sarcoidosis,
cysticercosis, trichinosis, and rheumatoid meningitis.
• Lumbar puncture (LP) is usually a safe procedure.
• Major complications: extremely uncommon, include
– cerebral herniation
– injury to the spinal cord or nerve roots
• Minor complications: greater frequency, include
– post-LP headache
– radicular pain or numbness.
Proper positioning of a patient in the lateral decubitus position. Note that the shoulders
and hips are in a vertical plane; the torso is perpendicular to the bed. [From RP Simon
et al (eds): Clinical Neurology, 7th ed. New York, McGraw-Hill, 2009.]
Positioning and site of Lumbar puncture
Contraindications to Lumbar Puncture:
• Infection in the skin overlying the access site(A)
• Bleeding diathesis
• Severe pulmonary disease or respiratory difficulty
• An altered level of consciousness.
• Patients with a focal neurologic deficit.
• A new-onset seizure.
• An immunocompromised state.
Collection of CSF from lumbar Puncture for analysis
Description of CSF Types
Fluid type WBC
cell tvpr Glucose
Normal <5 All
mg/dl or at
least 40% of
A 500–20,000 90% PMLs Low in most
B 25–500 Mononuclear
Low but may
C 5–1,000 Mononuclear
rarely quite low
Differential Diagnosis of Infectious
Causes of CSF Pleocytosis
Treatable by specific antimicrobial agents
• Type A fluid:
– Bacterial meningitis (pneumococcus, meningococcus, hemophilus,
streptococcus, listeria, etc.)
– Ruptured brain abscess
– Amebic meningoencephalitis
• Type B fluid
– Granulomatous meningitis
• Type C fluid
– Parameningeal infection
– Brain abscess
– Subdural abscess
– Cerebral epidural abscess
– Cerebral thrombophlebitis
– Spinal epidural abscess
– Retropharyngeal abscess
Differential Diagnosis (contd.)
• Listeria meningitis, Rickettsial meningitis
• Cerebral malaria
• Toxoplasmosis, Trypanosomiasis
• Toxic encephalopathy (associated with systemic bacterial infection)
• Viral infection (Herpes hominis type I encephalitis)
Not treatable by specific antimicrobial agents:
Type C fluid
• Postinfectious and postvaccinal encephalitis
• Viral meningitis (mumps, coxsackie, echovirus, lymphocytic
choriomeningitis, arboviruses, and others)
Differential Diagnosis of Noninfectious
Causes of CSF Pleocytosis
Ingestion of mercury or arsenic
Sarcoid (may produce type B CSF)
Tumor (leukemia most common; glucose can drop to zero)
Seizure activity (must diagnose only if other possibilities are ruled out and if
pleocytosis is minimal and rapidly clears)
CSF Comparison In Various Infections
Lymphocyte Protein Glucose
Causes of Brain edema
(cytotoxic) Interstitial (hydrocephalic)
Increased brain fluid due to
block of CSF absorption
Location of edema Chiefly white
white matter in
Edema fluid composition Plasma
Extracellular fluid volume Increased Decreased Increased
Capillary permeability to
large molecules (RISA, insulin)
Increased Normal Normal
radioisotope iodinated (125I) serum albumin (RISA)
Causes of Brain edema (contd.)
Vasogenic Cellular (cytotoxic)
Clinical disorders Brain tumor,
osmolality due to
EEG changes Focal slowing
Generalized slowing EEG often normal
Brain Edema: Role of drugs
Steroids Beneficial in brain
Not effective (?
Osmotherapy Reduces volume
of normal brain
volume acutely in
Acetazolamide ? Effect No direct effect Minor usefulness
Furosemide ? Effect No direct effect Minor usefulness
• Alzheimer’s disease (AD):
– Beta amyloid type Aβ42 is decreased probably because it
is deposited in plaques and is not available in a diffusible
– Total-tau (t-tau) and phosphorylated tau (p-tau) are both
increased in AD.
• Creutzfeldt-Jacob disease:
– Elevated CSF 14-3-3 in a patient with progressive dementia
of less than 2 years’ duration is considered a strong
indicator of CJD. A negative 14-3-3 test does not rule out
– Total-tau (t-tau) increased.
• General physiology: production, distribution, circulation; normal
pressure/biochemical/cellular values, cause for difference from plasma.
• Pathological changes: Pressure, clarity, colour, proteins (esp.IgG), glucose.
• Obtaining, collecting, analysing and storing a CSF sample.
• CSF types (based on pleocytosis), D/D based on types of CSF.
• CSF picture and comparison in various infectious categories.
• CSF biomarkers
• Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd
edition.Walker HK, Hall WD, Hurst JW, editors.Boston: Butterworths; 1990.
• PATHOLOGY 425 CEREBROSPINAL FLUID [CSF] at the Department of Pathology and
Laboratory Medicine at the University of British Columbia. By Dr. G.P. Bondy. Retrieved
• Normal Reference Range Table from The University of Texas Southwestern Medical
Center at Dallas. Used in Interactive Case Study Companion to Pathologic basis of
• Department of Chemical Pathology at the Chinese University of Hong Kong, in turn
citing: Roberts WL et al. Reference Information for the Clinical Laboratory. In Tietz
Textbook of Clinical Chemistry and Molecular Diagnostics, 4th edn. Burtis CA, Ashwood
ER and Bruns DE eds. Elsevier Saunders 2006; 2251 – 2318
• Ballabh P, Braun A, Nedergaard M. The blood-brain barrier: an overview. Structure,
regulation, and clinical implications. Neurobiol Dis 2004;16:1-13. PubMed
• Owens T, Bechman I, Engelhardt B. Neurovascular Spaces and the Two Steps to
Neuroinflammation. J Neuropathol Exp Neurol 2008; 67:1113-21. PubMed
• Aluise CD, Sowell RA, Butterfield DA. Peptides and Proteins in Plasma and Cerebrospinal
Fluid as Biomarkers for the Prediction, Diagnosis, and Monitoring of Therapeutic
Efficacy of Alzheimer’s disease. Biochim Biophys Acta 2008;1782:549-58 PubMed.
Selected examples of promising molecular markers for
Breast Cancer HER2
Lung Cancer HER2
Malignant Melanoma 9.2.27
Genitourinary Tumors (Ovarian) HER2
Head and Neck Cancers EGFR
Leukemia CD20, CD52
Lymphoma CD20, CD52