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Urinalysis & Body FluidsCLS 431

2ND Semester, 2015

Chapter 4: Cerebrospinal Fluid

(CSF)

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Cerebrospinal Fluid (CSF)

CSF

Cerebrospinal fluid (CSF) is surrounding the brain in the skull and the spinal cord in the spinal column.

Total volumes:– Adults:140 - 170 mL – Children: 10 - 60 mL

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Functions of CSF

-To protect the brain and the spinal cord from injury by acting as a fluid cushion.

It is the medium through which nutrients and the waste products are transported between brain/spinal cord and the blood.

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CSF

CSF is produce at the rate of 500 mL/day.

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Composition of CSF Blood brain barrier maintains the relative homeostasis of

CNS environment by tightly regulating the concentration of substances by specific transport systems for H+, K+, Ca2+, Mg2+, HCO3

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Glucose, urea and creatinine diffuse freely between blood and the CSF.

Proteins cross freely by passive diffusion along the concentration gradient

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Composition of Normal CSF

Protein - 15 - 45 mg/dL Glucose - 50 - 80 mg/dL Urea - 6.0 - 16 mg/dL Uric acid - 0.5 - 3.0 mg/dL Creatinine - 0.6 - 1.2 mg/dL Cholesterol - 0.2 - 0.6 mg/dL Ammonia - 10 – 35 μg/dL

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Composition of Normal CSF Sodium - 135 – 150 mEq/L Potassium - 2.6 – 3.0 mEq/L Chloride - 115 – 130 mEq/L Magnesium - 2.4 – 3.0 mEq/L Cells - 0 – 5 Lymph/μL

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Characteristics of normal CSF• Color - Colorless

• PH - 7.28 – 7.32

• Appearance - Clear

• Sp. Gravity - 1.003 – 1.004

• No clot formation on standing

• Total solids - 0.85 – 1.70 g/dL

• PO2 - 40 – 44 mmHg

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Processing• Approximately 15 - 20 cc fluid collected• Process within 1 hour without refrigeration - STAT

• Three tube set-up:– Tube 1: Chemistry and Immunology (Frozen)– Tube 2: Microbiology (Room temprature)

– Tube 3: Cell count, differential, cytology (Refrigerated)11

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Diagnosis by CSF

– Bacterial, TB, and fungal meningitis– Viral meningitis CNS syphilis, abscess– Meningeal malignancy

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Routine Lab TestsRequired

• Macroscopic Examination

• Total cell count and differential (stained)

• Glucose (CSF/plasma ratio)

• Protein

Optional

• Cultures, gram stain, antigens, cytology

• Protein electrophoresis, VDRL, D-dimers

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Gross Examination

• Normal CSF is clear, colorless

• Viscosity equal to water

• Viscous CSF with increased protein exudate

• Turbidity:– WBC > 200 cells/L– RBC > 400 cells/L– Microorganisms, increased protein

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Clot/Coagulation formationAllow the specimen of CSF to stand over night and

examine the sample for fibrin clot, which is formed if the sample contains fibrinogen.

Also note the nature of the clot.- Delicate clot, which resembles a cobweb, is seen in

tubercular meningitis due to marked increased in CSF proteins.

- The clot may have entrapped tubercle bacilli, which could be demonstrated microscopically by staining for acid-fast bacilli.

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Clot/Coagulation formation

Corase clot is formed in pyogenic meningitis,

in case of complete spinal block.

pH Determination. pH can be measured by using pH paper or using pH

meter.

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Xanthochromia• Pink, orange, or yellow discoloration

• RBC lysis or hemoglobin breakdown

• Oxyhemoglobin, bilirubin, increased protein

• Carotinoids, melanin

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Microscopic Exam of CSFTotal WBC Count

Normal CSF contains 0-8 lymph and no RBCs.

Procedure Glass slides Counting chamber Cover slip of thickness with size of 22 X 23 mm CSF diluting fluid – 1% Toludine blue or 1 % violet

– stains the WBC without lysing the RBC, thus enabling to count both RBC and WBC in Same chamber.

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• The stain is mixed with the CSF in the ratio 1:9 dil.

• Dilute acetic acid – 0.1 gm of crystal violet is added to 1 ml glacial acetic acid is made up to 50 ml by adding distilled water.

• Few drops of phenol is also added to this. As this fluid lyses the red cells it is useful in case of blood tinged CSF. In such case the RBC count estimated separately using undiluted CSF sample.

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Procedure Dilution – if CSF is clear there is no need for

dilution and both RBS and WBC can be counted simultaneously in the same chamber.

If CSF is cloudy then make a dilution of 1:10 or 1:20.

One can also pipette out 900μL of CSF diluting fluid in the tube and 100μL of CSF to it.

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Counting of cells• Charge the counting chamber properly

without any air bubbles.

• Wait for 5 minutes before counting, to allow the cells in CSF to settle down.

• Count the cells in all 9 squares by using low power objective.

Calculation

WBC in CSF/cumm(μL)=No.of cellˣdep.ˣdilu.

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Important point• Cells in CSF should be counted immediately with

out delay to prevent degeneration of cells which will give false low counts.

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Reference Intervals for CSF

Cell type Adults(%) Neonates(%)

Lymphocytes 62 20 Monocytes 36 72 Neutrophils 2 3 Histiocytes Rare 5 Ependymal Rare Rare Eosinophils Rare Rare

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Increased Neutrophils in CSF

• Meningitis (bacterial, early TB, fungal)

• Other infections

• Following CNS hemorrhage

• Following CNS infarct

• Foreign materials

• Metastatic tumor

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Increased Lymphocytes in CSF

• Meningitis (aseptic, viral, Listeria monocytogenes )

• Parasitic infections

• Degenerative disorders

– Encephalopathy due to drugs

• Other inflammatory conditions

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Plasmacytosis in CSF• TB meningitis

• Syphilitic meningitis

• Parasitic infection

• Acute viral infections

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Eosinophilic pleocytosis in CSFCommonly associated with:

• Parasitic infections

• Fungal infections

• Reaction to foreign material

Infrequently associated with

• Bacterial or tuberculous meningitis

• Viral, rickettsial infection, lymphoma, sarcoidosis

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Chemical Analysis Total protein non-specific marker of disease

• 300 different proteins have been isolated from CSF using two-dimensional electrophoresis and silver staining

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Conditions Associated with Increased CSF Total Protein

• Increased blood-CSF permeability– Meningitis (bacterial, fungal, TB)– Hemorrhage– Endocrine disorders– Mechanical obstruction (tumor, disc, abcess)– Neurosyphilis

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Glucose estimation in CSF• CSF glucose is derived from blood glucose hence,

ideally CSF glucose level should be compared with fasting plasma glucose level for adequate clinical interpretation.

• Clinical Significance.

• CSF glucose less than 40 mg/dL or CSF/plasma glucose less than 0.3 are considered abnormal

(normal CSF/Plasma glucose ratio may very from 0.3 – 0.9)

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• Increased CSF glucose is of no clinical significance.

• Causes of decreased CSF glucose

• Meningitis-Bacterial, fungal tubercular and syphilitic meningitis.

• Tumors.

• Cerebral ameobiasis.

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Bacterial Meningitis

• Listeria monocytogenes common in newborns, elderly, and other immunocompromised hosts

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Bacterial Meningitis

• Gram’s stain sensitivity = 60 - 90%

• Depends on organism, experience,

• Culture sensitivity = 80 - 90%

• Latex agglutination becoming more widely used due to simplicity and accuracy

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Test Appearance Pressure WBC/μL Protein mg/dL

Glucose mg/dL

Chloride

Normal CSF

Clear 90 – 180 mm

0-8 lymph. 15-45 50-80 115-130 mEq/L

Acute bacterial meningitis

Turbid Increased 1000 -10000

100 – 500 < 40 Decreased

Viral meningitis

Clear Normal to moderate increase

5-300, rarely >1000

Normal to mild increased

Normal Normal

Tubercular meningitis

Slightly opaque cobweb formation

Increased/ decreased, spinal block

100-600 mixed or lymph.

50-300 due to spinal block

Decreased Decreased

Fungal meningitis

Clear Increased 40-400 mixed

50-300 Decreased Decreased

Acute syphilitic

Clear Increased About 500 lymph

Increased but <100

Normal normal

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Bacterial Meningitis

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Neurosyphilis

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