Cerebrospinal Fluid (CSF) Fundamentals (copy)

Purpose and Formation of Cerebrospinal Fluid (CSF)

  • Purpose: CSF cushions the central nervous system and transports nutrients.

  • Formation: CSF is formed through a selective filtrate process, primarily in the choroid plexus.

The Blood-Brain Barrier (BBB)

  • Purpose: The BBB prevents unrestricted interchange between blood plasma and CSF, serving as a protective shield.

  • Characteristics: It blocks certain substances (bacteria, large proteins) and permits others (glucose, specific drugs) to pass.

Clinical Collection and Handling of CSF

  • Tube Draw Sequence: Typically, 3 to 4 tubes are collected in the following order:

    1. Tube #1: Chemistry

    2. Tube #2: Microbiology

    3. Tube #3: Hematology

    4. Tube #4: Reserve or Reference

  • Why CSF is Treated STAT: Samples are treated as immediate priority due to critical patient care needs, as White Blood Cells (WBCs) can lyse quickly.

Visual Assessment and Physical Appearance

  • Bloody Appearance: Can indicate a hemorrhage or a traumatic tap.

  • Hemorrhage vs. Traumatic Tap:

    • Traumatic Tap: Blood is most pronounced in Tube 1 and decreases in further tubes.

    • Hemorrhage: Blood is evenly distributed across all tubes.

  • Xanthochromic: Yellow tint indicating old hemorrhage.

  • Cloudy Appearance: Suggests infection or high cellular content.

CSF Chemistry Analysis

  • Glucose Values: Normal CSF glucose is approximately 2/32/3 of plasma glucose. Pathological indications include levels less than 40 mg/dL40 \, mg/dL indicating bacterial meningitis.

  • Protein Levels: Normal range is 15−45 mg/dL15-45 \, mg/dL; elevated levels often indicate meningitis or other brain issues.

CSF Microbiology

  • Overall Purpose: Essential for identifying meningitis causative agents.

  • Bacterial Identification: Methods include Gram stain, Culture, and PCR.

  • Fungal Identification: Fungal tests can include India ink and immunoassays, especially relevant for immunocompromised patients.

Cellular Components and Counts

  • Normal WBC and RBC Values: WBC count of 0-5 \, \text{cells/}L (microliter); RBC count should be zero.

  • Elevated WBCs: Known as Pleocytosis, indicating potential infections such as meningitis, with specifics varying by types of cells present:

    • Neutrophils: Associated with bacterial meningitis.

    • Lymphocytes: Indicative of viral meningitis.

    • Eosinophils: Suggests tubercular fungal infections, parasitic infections, or response to shunts.

    • Macrophages: Present after hemorrhage for debris cleanup.