Cerebrospinal Fluid (CSF) Fundamentals (copy)

Cerebrospinal Fluid (CSF) Purpose

CSF cushions the central nervous system and transports nutrients.

CSF Formation

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

Blood-Brain Barrier (BBB) Purpose

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

Characteristics of the BBB

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

Tube Draw Sequence for CSF Collection

Typically, 3 to 4 tubes are collected: Tube #1 (Chemistry), Tube #2 (Microbiology), Tube #3 (Hematology), Tube #4 (Reserve or Reference).

Why is CSF Treated STAT?

Samples are treated as immediate priority due to critical patient care needs, as White Blood Cells (WBCs) can lyse quickly.

Bloody Appearance of CSF

Can indicate a hemorrhage or a traumatic tap.

Traumatic Tap vs. Hemorrhage

In a traumatic tap, blood is most pronounced in Tube 1 and decreases in further tubes. In hemorrhage, blood is evenly distributed across all tubes.

Xanthochromic CSF

Yellow tint indicating old hemorrhage.

Cloudy Appearance of CSF

Suggests infection or high cellular content.

Normal CSF Glucose Values

Normal CSF glucose is approximately $2/3$ of plasma glucose; levels less than $40 \text{ mg/dL}$ indicate bacterial meningitis.

Normal CSF Protein Levels

Normal range is $15-45 \text{ mg/dL}$; elevated levels often indicate meningitis or other brain issues.

Purpose of CSF Microbiology

Essential for identifying meningitis causative agents.

Methods of Bacterial Identification in CSF

Methods include Gram stain, Culture, and PCR.

Fungal Identification Tests in CSF

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

Normal WBC and RBC Values in CSF

WBC count of $0-5 \text{ cells/}\text{L}$ (microliter); RBC count should be zero.

Elevated WBCs in CSF

Known as Pleocytosis, indicating potential infections such as meningitis.

Neutrophils in CSF

Associated with bacterial meningitis.

Lymphocytes in CSF

Indicative of viral meningitis.

Eosinophils in CSF

Suggests tubercular fungal infections, parasitic infections, or response to shunts.

Macrophages in CSF

Present after hemorrhage for debris cleanup.