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CSF ANALYSIS. CSF Formation. Cerebrospinal fluid (CSF) is the liquid that surrounds the brain & spinal cord. The brain & spinal cord are surrounded by the meninges that consist of three layers: dura matter, arachnoid & pia matter

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csf formation
CSF Formation

Cerebrospinal fluid (CSF) is the liquid that surrounds the brain & spinal cord.

The brain & spinal cord are surrounded by the meninges that consist of three layers:

dura matter, arachnoid & pia matter

  • CSF flow between the arachnoid & pia matter in an area referred to as the subarachnoid space
  • The cerebrospinal fluid is formed mainly in the choroid plexuses of

the lateral, third, and fourth ventricles;

  • some originates from the ependymal cells lining the ventricles
  • and from the brain substance
  • Normal blood brain barrier is important for the normal chemistry results of CSF
  • Mechanism of formation:
    • Selective ultrafiltration of plasma
    • Active secretion by epithelial membranes
functions of csf
Functions of CSF

1- Physical support & protection of the CNS from trauma.

2- Supplying nutrients to the CNS & removal of metabolic wastes from CNS

3- Intra-cerebral transport (neuroendocrine role i.e. distribution of hypothamic hormones within the brain)

clinical indications for csf analysis
Clinical Indications for CSF Analysis

CSF is performed in cases of suspected:

1- CNS infections (infectious meningitis & encephalitis)

2- CNS malignancy (as malignant infiltrates as in leukemia ..etc)

3- CNS hemorrhages (as subarachnoid hemorrhage)

4- CNS demyelinating diseases (as multiple sclerosis)

routine laboratory csf analysis
Routine Laboratory CSF Analysis


Lumbar puncture

At interspace of vertebrate L3-4 or lower

With complete aseptic techniques


Collected CSF sample is immediately divided into three tubes:

Tube 1: Chemical Investigation (kept in freezer till performed)

Tube 2: Microbiology Investigation (kept in room temperature)

Tube 3: Microscopic Investigation (Cellular Counting – Differential – Cytology)

physical examination of csf
Physical examination of CSF

Normal CSF: Clear & colorless

Viscosity: equal to water (increased with increased proteins)

Color and/or turbidity of CSF: observed only in pathological circumstances.

Turbid CSF

Bacteria, WBCs cells or pus cells: suggestive of a CNS infection (menigitis or encephalitis)

Blood : suggestive of hemorrhage: subarachnoid or artifactual traumatic tap: DIFFERNTIATE?

physical examination of csf1
Physical examination of CSF

Red & brown color :


Yellow colour

1-Jaundice (bilirubin in CSF)

2- Xanthochromia (hemoglobin breakdown pigments in CSF)

Xanthochromic CSF suggests that a subarachnoid hemorrhagehas recently occurred

(at least within two hours prior to tapping).

The yellow color is due to bilirubin generated in the CNS by the breakdown of hemoglobin released from RBC's. (so jaundice should be excluded).

microscopic examination of csf
Microscopic examination of CSF


Normal Total WBCs count: 1-5 lymphocytes /HPF

Normal differential WBCs Count: (in centrifuged cells)

- 62% lymphocytes

- 36% monocytes

- 2% neutrophils

Increased neutrophils: bacterial meningitis

Increased lymphocytes: aseptic and viral meningitis


Normally CSF is blood free

RBCs in CSF: subarachnoid hemorrhage & malignancy

Artifact: traumatic tap (should be excluded)

(Traumatic tap bright red color RBCS in decreasing number as the fluid is sampled)

chemical examination of csf
Chemical examination of CSF
  • In addition to the major ions, CSF contains oxygen, sugars (e.g. glucose, fructose), lactate, proteins (e.g. albumin, globulins), amino acids, urea, ammonia, glutamine, creatinine, lipids, hormones (e.g. insulin) and vitamins.
csf glucose
CSF Glucose
  • Normal CSF glucose: 50-80 mg/dl
  • - The actual CSF glucose concentration may be:
  • 1- Falsely low in the presence of hypoglycemia
  • Or 2- Incorrectly interpreted as normal when the patient is hyperglycemic
  • Accordingly, CSF glucose should always be compared with a simultaneous
  • plasma glucose that is drawn prior to lumbar puncture.
  • Normal CSF glucose/ plasma glucose ratio is approximately 0.6-0.7
  • (N.B. Ratio is decreased if plasma glucose is more than 500 mg/dl
  • due to saturation of the glucose carrier system to CSF
csf glucose cont
CSF Glucose cont.

Elevated CSF / plasma glucose ratio (more than 0.7)

has no CSF diagnostic significance (occurs with hyperglycemia)

Decreased CSF / plasma glucose ratio(hypoglycorrhachia):

1- CNS septic (pyogenic) infections

Due to increased glycolysis by leukocytes and bacteria (with increase CSF lactate)

2- Brain tumors

due to increased metabolism of glucose by CNS

3- TB meningitis & sarcoidosis

Due to inhibition of glucose entry into the subarachnoid space

N.B. in viral CNS infections, CSF glucose is usually normal

csf protein cont
CSF Protein cont.

Lumbar CSF protein: 15 - 45 mg/dl (mostly albumin)

The majority of CSF protein is derived from the plasma by ultrafiltration

Certain proteins arise within the intrathecal compartment:

1- Immunoglobulinsproduced by CNS lymphocytes

2- Transthyretin(produced by choroid plexus)

3- Various structural proteins found in brain tissue

csf protein
CSF Protein
  • Decreased CSF protein:
  • Leak of CSF from a tear in the dura due to severe trauma
  • 2- Otorrohea: leak of CSF from ear
  • 3- Rhinorrohea: leak of CSF from nose
csf protein cont1
CSF Protein cont.

Increased CSF protein:

1- Lysis of contaminant blood from traumatic tap

2- Increased permeability of epithelial membrane (blood-brain barrier)

in cases of:

- CNS bacterial or fungal infections

- Cerebral hemorrhages

2- Increased production by CNS tissue as in cases of:

- Multiple sclerosis (MS)

- Subacute sclerosing panencephalitis (SSPE)

3- Obstruction as in cases of :

- Tumors or abscess

csf protein cont2
CSF Protein cont.

Analysis of protein fractions: (Albumin & IgG)

  • 1- Albumin of CSF

is obtained from blood by means of blood-brain barrier (as it is

produced solely by the liver)

In cases of increased permeability of BBB, albumin is increased in


  • 2- IgG of CSF can be obtained:

from blood (By BBB) : increase in cases of increase permeab. of BBB

& by local synthesis from plasma cells within CSF (increased in cases of MS)

So, it is essential to determine the source of IgG


csf protein cont3
CSF Protein cont.

BY CSF / serum albumin index calculation

CSF serum albumin index = CSF albumin (mg/dl) / serum albumin (g/dl)

Index less than 9 indicates intact BBB (no increased permeability of BBB)


CSF IgG / Serum IgG

CSF IgG index = ---------------------------------------

CSF albumin / serum albumin

Normal : less than 0.7

Increased in cases of demylineating diseases of CNS as : Multiple sclerosis (MS)

csf immunoglobulin
CSF Immunoglobulin

CSF IgG can arise:

from plasma cells within CSF

& from the blood through BBB

↑CSF [IgG] without concomitant ↑ in CSF [Alb] suggests local production of IgG:

multiple sclerosis (MS)

subacute sclerosing panencephalitis (SPEE)

CSF IgG/Serum IgG

CSF IgG index:

Normally: < 0.7


CSF serum /Albumin index

csf lactate
CSF lactate

CSF lactate is increased in cases of bacterial meningitis (due to increased glycolysis by bacteria & inflamatory cells)

csf glutamine
CSF glutamine

The level of CSF glutamine reflects level of ammonia in that is normally removed in the CNS by formation of glutamine (amino acid glutamate + ammonia).

Glutamine synthesis helps to protect the CNS from the toxic effects of increased ammonia.

Ammonia production is increase dramatically in patients with liver failure.

Accordingly, CSF glutamine production is increased in cases of hepatic encephalopathy

enzymes in the csf
Enzymes in the CSF

CSF lactate dehydrogenase (LDH) may be elevated in bacterial meningitis.

CSF adenosine deaminase (ADA) elevations can occur in tuberculous meningitis.

other chemical components of csf
Other Chemical Components of CSF

CSF [Calcium], [Potassium] & [Phosphates] are lower than their levels in the blood

CSF [Chloride] & [Magnesium] are higher than their levels in the blood

Abnormal CSF [Chloride]

marked  in acute bacterial meningitis

slight  in viral meningitis & brain tumors