IG

Module-7-CSF

Module 7: Examination of Cerebrospinal Fluid

A. Introduction

  • Cerebrospinal fluid (CSF): A major fluid of the body.

    • Functions:

      • Supplies nutrients to nervous tissue.

      • Removes metabolic waste.

      • Provides a mechanical barrier to cushion the brain and spinal cord against trauma.

B. Formation and Physiology

  • Production:

    • CSF is produced in the choroid plexuses of the two lumbar ventricles and the third and fourth ventricles.

    • Approximately 20 mL produced every hour in adults.

  • Flow and Volume:

    • Flows through the subarachnoid space between the arachnoid and pia mater.

    • Maintains a volume of 90 to 150 mL in adults and 10 to 60 mL in neonates.

    • Circulating fluid reabsorbed back into blood capillaries via arachnoid granulations/villae at a rate equal to its production.

C. Cerebrospinal Fluid (CSF)

  • Location: Fluid in the sub-arachnoid space between the arachnoid and pia mater.

  • Functions:

    • Protects CNS tissues: Central Nervous System.

    • Acts as a mechanical buffer to minimize trauma.

    • Regulates intracranial pressure volume.

    • Circulates nutrients and removes metabolic waste products.

    • Serves as a lubricant.

  • Composition: Similar to plasma but has:

    • Less protein

    • Less glucose

    • More chloride ions

D. Specimen Collection and Handling

  • Maximum volume of CSF:

    • Adults: 90-150 mL

    • Neonates: 10-60 mL

  • Formation Rate:

    • 450-750 mL per day or 20 mL per hour, reabsorbed to maintain constant volume.

  • Collection Procedure:

    • Collected via lumbar puncture by experienced medical personnel.

    • About 1-2 mL collected for examination.

    • Collected between the third, fourth, or fifth lumbar vertebra under sterile conditions.

    • Specimens collected in three sterile tubes labeled 1, 2, and 3:

      • Tube 1: Chemistry and Serology.

      • Tube 2: Microbiology laboratory.

      • Tube 3: Hematology.

  • Optional 4th Tube: For microbiology to assess skin contamination or additional serologic testing.

  • Care in handling due to potential complications.

  • Ideally, tests performed on a STAT basis:

    • Chemistry and serology tubes frozen.

    • Microbiology tubes remain at room temperature.

    • Hematology tubes refrigerated.

E. Reporting and Interpretation

  • Observe specimen appearance as soon as it reaches the laboratory:

    • Normal CSF: Appears clear and colorless.

    • Cloudy/Milky/Turbid:

      • Indicates high protein or lipid concentration;

      • May suggest infection due to the presence of WBCs.

      • Purulent CSF indicates pus cells, suggestive of acute bacterial meningitis.

  • Blood in CSF:

    • Likely from a traumatic lumbar puncture or central nervous system hemorrhage.

    • In traumatic puncture, sample No. 1 often has more blood than sample No. 2.

    • Following subarachnoid hemorrhage, CSF may appear xanthrochromic (pink, orange, or yellow) due to RBC degradation products.

F. CSF Analysis

  • Examination:

    • Visually and microscopically analyzed.

    • Total number of cells counted and identified:

      • Physical Examination:

        • Color

        • Turbidity

  • The third tube's cells must be counted within 1 hour of collection (cells disintegrate rapidly); otherwise, store at 2-8°C.

  • Cell Counting Procedure:

    1. Mix 1 drop of CSF with 1 drop of toluidine blue diluting fluid.

    2. Use a modified Fuchs-Rosenthal ruled counting chamber or a Neubauer chamber.

    3. Fill chamber with diluted CSF via a fine bore pipette, ensuring no overflow.

    4. Wait 2 minutes for cells to settle.

    5. Count cells microscopically focusing on cells and rulings.

  • Calculation:

    • Standard Neubauer formula for determining number of cells per microliter.

    • For counting clear specimens, count undiluted if no overlapping observed; otherwise, use calibrated pipettes and normal saline for dilutions.

G. Clinical Significance

  • Used in diagnosing:

    • Meningitis of various origins (bacterial, fungal, mycobacterial, amoebic).

    • Differential diagnosis of other infectious diseases.

    • Subarachnoid hemorrhage or intracerebral hemorrhage.

H. Predominant Cells in CSF

  • Lymphocytes:

    • Normal

    • Associated with viral, tubercular, fungal meningitis, and multiple sclerosis.

  • Neutrophils:

    • Associated with bacterial meningitis and early viral/tubercular/fungal meningitis; cerebral hemorrhage.

  • Monocytes:

    • Normal; linked with viral, tubercular, fungal meningitis, and multiple sclerosis.

  • Macrophages:

    • Related to RBCs in spinal fluid.

  • Blast forms:

    • Indicative of acute leukemia.

  • Lymphoma cells:

    • Suggests disseminated lymphomas.

  • Plasma cells:

    • Associated with multiple sclerosis and lymphocyte reactions.

  • Ependymal, choroidal, and spindle-shaped cells:

    • Relevant in diagnostic procedures.

  • Malignant cells:

    • Indicative of metastatic carcinomas and primary CNS carcinoma.

      Microglial cells: Act as the brain's immune defense, responding to injury and disease.

Normal CSF Adult Lab Ranges

  • CSF Volume: 90-150 mL

  • Production Rate: 450-750 mL per day or 20 mL per hour

  • Appearance: Normal CSF appears clear and colorless.

  • White Blood Cells (WBCs): Normal count is generally <0-5 WBCs per microliter.

  • Blood Cells (RBCs): Normal count is generally <5 RBCs per microliter.

  • Protein Levels: Normal protein concentration is usually less than 10-45 mg/dL.

  • Glucose Levels: Normal glucose concentration typically ranges from 40-70 mg/dL, about two-thirds of serum glucose levels.

  • Chloride Levels: Normal chloride concentration is approximately 118-132 mmol/L.

  • Potassium Levels: Normal potassium concentration generally falls between 3.5-5.0 mmol/L.