MN

CSF and Spinal Fluid - Vocabulary Flashcards (Chapter 1-6)

CSF Physiology, Collection, and Diagnostic Testing

  • CSF overview

    • CSF is produced by the choroid plexus and secreted into the ventricles of the brain.
    • It circulates through the brain, brainstem, and spinal cord, then enters the subarachnoid spaces.
    • CSF can be absorbed into the bloodstream via arachnoid granulations.
    • Obstruction of CSF outflow leads to hydrocephalus (water on the brain), an abnormal accumulation of CSF that increases intracranial pressure and can cause brain damage, stroke, infection, or imbalance between production and absorption of CSF.

  • Blood–brain barrier (BBB)

    • BBB consists of capillary endothelium with very tight junctions that restrict crossing from blood into the brain.
    • This selective barrier prevents many substances in blood from entering CNS tissue.
    • Note: in newborns, the skull/BBB is not fully formed yet, so there is increased permeability risk.
    • Importance: protects neural tissue from potentially harmful blood-borne substances.

  • Anatomical context (CSF flow and meninges)

    • CSF is produced in the choroid plexus, flows through ventricles, coats the brain and spinal cord, and enters the subarachnoid space.
    • Arachnoid granulations provide a pathway for CSF to re-enter the bloodstream.
    • Meninges surrounding the brain/spinal cord: dura mater (outer) → arachnoid (middle, web-like) → pia mater (inner, adherent to neural tissue).
    • The CSF resides in the subarachnoid space between the arachnoid and pia mater.

  • Lumbar puncture (LP) and specimen collection

    • LP is performed by a physician or anesthesiologist; medical laboratory scientists assist with collection but do not perform the LP.
    • LP purpose: aseptic puncture into the spinal subarachnoid space to collect CSF; opening pressure is recorded.
    • Typical CSF collection volume: about $15-20\,\text{mL}$, which may be less for pediatric patients.
    • Ideal specimen collection is 3–4 tubes; each tube has different testing priorities:
    • Tube 1: chemistry tests (e.g., protein, glucose, lactate).
    • Tube 2: microbiology (Gram stain, culture, antigen testing).
    • Tube 3: hematology and cell counts (cell counts, differential).
    • Tube 4 (optional): additional cell counts or special testing as needed.
    • In practice, all CSF tests are run STAT to avoid false results and to prevent degradation or changes in composition.
    • If the physician has limited CSF volume, prioritize tests requested; discuss with the physician which tests are essential.
    • If CSF is collected in a single small container, microbiology testing should be performed first to minimize contamination, followed by cell counts, then chemistry.
    • After collection, the physician closes the puncture and rechecks opening pressure; closing pressure is recorded.
    • The lab workflow emphasizes immediate delivery to the lab and fast processing to avoid falsely low cell counts or falsely high lactate levels.

  • Physical examination of CSF (in the lab)

    • Color: CSF is normally colorless and has a viscosity similar to water.
    • Clarity: typically clear; cloudy CSF suggests increased white blood cells, red blood cells, microorganisms, or high protein.
    • Xanthochromia: yellow, orange, or pink color due to bilirubin or other breakdown products; indicates prior blood breakdown or other pathologies.
    • If a sample is oddly colored, correlate with centrifugation findings and clinical context to differentiate traumatic tap from intrathecal pathology.

  • Traumatic tap vs hemorrhage (color and clarity differentiation)

    • Traumatic tap: cannulation-related blood that decreases across tubes (e.g., tube 1 bloody, tube 2 less, tube 3 clear).
    • Hemorrhage (intrathecal bleed): blood persists across multiple tubes and may become even red after centrifugation; not cleared by subsequent tubes.
    • Centrifugation can help distinguish: if the red color clears in later tubes or if the red pellet persists in all tubes, this supports hemorrhage rather than traumatic tap.

  • Initial CSF handling and processing signals

    • The first step in the lab is a physical examination of CSF (color, clarity, xanthochromia).
    • Then proceed with cell counts, chemistry, and microbiology testing as indicated.
    • If volumes are limited, prioritize microbiology to reduce contamination, followed by cell counts, then chemical testing.

  • Cellular (microscopic) analysis and differential counts

    • Cell counting is typically performed with a hemocytometer.
    • Normal CSF has very low cellularity; expected white blood cells (WBC) are roughly 0–5 cells/µL.
    • Red blood cell (RBC) counts are usually very low or zero in normal CSF.
    • If dilution is needed due to bloody CSF, a dilution factor is used in calculations; refer to the hemocytometer counting protocol.
    • Pleocytosis: an increased number of cells in CSF; commonly reflects infection or inflammation.
    • Differential interpretations for WBCs in CSF:
    • Neutrophils: suggest bacterial meningitis; may also appear in TB, fungal, or parasitic infections in some contexts.
    • Lymphocytes: suggest viral meningitis; can also be seen in TB, fungal, or syphilitic infections.
    • Plasma cells: abnormal in CSF; may indicate MS, viral infections, acute or chronic inflammatory conditions.
    • When interpreting counts, consider the total CSF WBC count together with the differential and the clinical picture.
    • Image-based morphology notes (described in slides):
    • Macrophages with vacuoles; cytoplasm often slightly more purple; nuclei appear clumped/condensed.
    • Neutrophils: phagocytic with condensed nuclei; may contain bacteria when present.
    • Eosinophils: increased in parasitic infections, fungal infections, or allergic reactions.
    • Erythrophages and siderophages: macrophages that have engulfed red blood cells or breakdown products (iron-containing) from blood; Prussian blue stain helps identify siderophages.
    • Plasma cells: eccentric nucleus, halo; seen in MS and certain inflammatory conditions.
    • Rare cells: malignant cells and choroid plexus cells may be found in CSF cytology in certain disease states.
    • Cytospin artifacts: some cells may resemble unusual shapes; scanning the whole slide is important to avoid misidentification.
    • Summary of cell types and associations:
    • Bacterial meningitis: neutrophils increased
    • Viral meningitis: lymphocytes increased
    • Chronic inflammatory conditions, MS: plasma cells increased
    • Parasitic/fungal infections and allergies: eosinophils increased
    • Hemorrhage: RBCs increased; macrophages present with erythrophagocytosis; hemosiderin may be seen
    • Malignancy: malignant cells detected

  • Chemical examination of CSF

    • Protein
    • Normal CSF protein concentration is about
      15\text{ to }45\ \text{mg/L}
      (often cited as mg/dL in some references; use whichever unit your lab reports but remember the value range).
    • CSF/serum protein comparison: CSF protein is typically about 1/1000 of serum protein.
    • Causes of abnormal CSF protein:
      • Leaking CSF (traumatic tap or CSF leak) can alter protein levels.
      • Meningitis and multiple sclerosis can increase CSF protein.
      • Traumatic tap (blood contamination) can transiently increase protein.
    • Albumin and IgG indices
    • Albumin in CSF reflects barrier permeability; IgG reflects intrathecal synthesis.
    • CSF albumin index (QALB): Q{Alb} = \frac{[\text{Albumin}]{CSF}}{[\text{Albumin}]{serum}}
      • Normal: $Q{Alb} < 9$; Mild impairment: $9 \le Q{Alb} < 14$; Moderate impairment: $14 \le Q{Alb} < 100$; Severe impairment: $Q{Alb} \ge 100$.
    • IgG index: a measure of intrathecal IgG synthesis, often calculated as \text{IgG index} = \frac{\frac{[}\text{IgG}]{CSF}}{\frac{[}\text{IgG}]{serum}}}{\frac{[}\text{Albumin}]{CSF}}{[\text{Albumin}]{serum}} = \frac{Q{IgG}}{Q{Alb}}
      • Normal range: approximately 0.3 \le \text{IgG index} \le 0.7.
      • An elevated IgG index or elevated CSF IgG with other supporting data suggests intrathecal IgG synthesis, as seen in inflammatory/infectious conditions (e.g., MS).
    • CSF protein electrophoresis
    • Four main bands are typically observed: albumin, prealbumin (transthyretin), and two transferrin bands.
    • Oligoclonal bands (OCBs) may appear in the gamma region and are indicative of intrathecal IgG synthesis; their presence is strongly associated with multiple sclerosis and other inflammatory CNS diseases.
    • A normal CSF electrophoresis shows the baseline bands with no extra gamma-region bands; MS may show oligoclonal bands in CSF not present in serum.
    • Myelin basic protein (MBP)
    • MBP can be elevated in MS and may be used to assess disease activity/progression.
    • Glucose
    • CSF glucose normally ranges from about 0.60\text{-}0.70 of the corresponding serum glucose:
      \text{CSF glucose} \approx 0.60\text{ to }0.70 \times [\text{Serum glucose}]
    • Decreased CSF glucose is common in meningitis (especially bacterial) and with tumors; hyperglycemia can raise CSF glucose proportionally.
    • A traumatic tap can also affect the CSF glucose reading depending on sample handling and timing.
    • Lactate
    • Normal CSF lactate typically falls in the range 10\text{-}22\ \text{mg/dL} (values may be reported in mmol/L in some labs).
    • Elevated CSF lactate indicates conditions with impaired CNS oxygen delivery or metabolism (e.g., cerebral infarction, intracranial hemorrhage, meningitis, traumatic brain injury, hydrocephalus).
    • In viral meningitis, lactate tends to be lower (e.g., < (30\ \text{mg/dL})); in bacterial and other meningitides, lactate is often markedly elevated (e.g., > (35\ \text{mg/dL})).
    • Microbiologic testing
    • Gram stain: detects bacterial organisms directly on CSF.
    • Acid-fast stain: used for Mycobacterium tuberculosis and other mycobacteria.
    • India ink stain: used for Cryptococcus neoformans when fungal meningitis is suspected.
    • Spun sediment/cytocentrifugation: CSF is concentrated for more reliable microscopic examination and staining.
    • Cultures: bacterial, fungal, and occasionally mycobacterial cultures; blood cultures are often drawn concomitantly.
    • PCR and antigen testing: increasingly used; panels may detect viral meningitis pathogens; latex agglutination, EIA, and RA-based methods are used for specific antigens.
    • Common etiologies and testing approaches:
      • Bacterial meningitis: culture and Gram stain; rapid antigen tests when available; PCR panels for common bacteria.
      • Viral meningitis: viral cultures less common now; PCR panels increasingly used.
      • Fungal meningitis: fungal cultures and antigen testing (e.g., cryptococcal antigen); PCR may be used.
      • Parasitic meningitis: wet mounts or specialized testing; consider Naegleria fowleri in appropriate clinical contexts.
    • Special examples mentioned: Naegleria fowleri as an emerging/deadly parasitic infection; cryptococcal infection detected via India ink and cryptococcal antigen testing.
    • Other practical/special tests
    • Molecular methods (PCR): expanding role in identifying pathogens and CNS inflammatory conditions.
    • “MS panel” or multiple sclerosis-related testing may refer to oligoclonal band analysis and related intrathecal synthesis assessments.
    • Treponema pallidum (syphilis) testing, herpes simplex virus testing, and broader CNS infection panels may be available.
    • Additional chemical tests: sodium and chloride in CSF measurements may be performed as part of routine chemistry panels.

  • Practical workflow and clinical implications

    • CSF testing is performed as a rapid, integrated set of analyses to guide treatment decisions, especially in suspected meningitis or other CNS infections.
    • When CSF volume is limited, clinicians and laboratorians must prioritize tests that will most influence patient management (e.g., microbiology first, followed by cell counts, then chemical testing).
    • Interpretation of CSF results requires considering the entire clinical context: patient age, symptoms, imaging, and concomitant laboratory data (serum glucose, albumin, IgG, etc.).
    • The presence of particular cellular patterns (neutrophils vs lymphocytes vs plasma cells) helps distinguish bacterial from viral and other etiologies, but overlaps exist; corroborative data (lactate, glucose, protein, imaging) improves accuracy.

  • Summary of key relationships and diagnostic clues

    • Bacterial meningitis: neutrophilic pleocytosis, elevated protein, low to normal glucose, elevated lactate; Gram stain and culture frequently positive; urgent treatment required.
    • Viral meningitis: lymphocytic pleocytosis, normal or mildly elevated protein, normal or near-normal glucose, normal or slightly elevated lactate.
    • TB/fungal meningitis: lymphocytic predominance with elevated protein; LDH and glucose changes may occur; specialized stains and cultures or PCR needed.
    • MS and inflammatory CNS diseases: oligoclonal bands in CSF, elevated IgG index, possible MBP elevation; plasma cells may be present in CSF cytology.
    • Hemorrhage: elevated RBCs in CSF with macrophages showing erythrophagocytosis; differentiate from traumatic tap by serial tube results and centrifugation findings.
    • Malignancy: presence of malignant cells in CSF cytology; may co-occur with inflammatory features.