CSF (Textbook) Flashcards
Meninges Layers
Three layers: the dura mater, the arachnoid, and the pia mater
- Dura mater: outer layer that lines the skull and vertebral canal
- Arachnoid: is a filamentous (spider-like) inner membrane
- Pia mater: is a thin membrane lining the surfaces of the brain and spinal cord
Spinal Tap Tube Order
- Tube 1: is used for chemical and serologic tests because these tests are least affected by blood or bacteria introduced as a result of the tap procedure
- Tube 2: is usually designated for the microbiology laboratory
- Tube 3: is used for the cell count, because it is the least likely to contain cells introduced by the spinal tap procedure.
- A fourth tube may be drawn for the microbiology laboratory to rule out contamination by skin flora
CSF Specimen Preservation
- Hematology tubes are refrigerated.
- Microbiology tubes remain at room temperature.
- Chemistry and serology tubes are frozen.
Clotting in CSF Specimens
Fluid collected from a traumatic tap may form clots owing to the introduction of plasma fibrinogen into the specimen. Bloody CSF caused by intracranial hemorrhage does not contain enough fibrinogen to clot.
Cell Stability in CSF
WBCs (particularly granulocytes) and RBCs begin to lyse within 1 hour, and 40% of the leukocytes disintegrate after 2 hours
CSF Cell Counts
An improved Neubauer counting chamber (Fig. 9–5) is routinely used for performing CSF cell counts
Calculation:
(Number of cells counted × dilution)
(Number of cells counted × volume of 1 square)
= cells/µl
Cell Count Dilution Prep
- Made with normal saline, mixed, and loaded into the hemocytometer.
- Cells are counted in the four corner squares and the center square on both sides
- To count specifically WBCs, substitute 3% glacial acetic acid to lyse the RBCs
Cell Count Prep on Non-Diluted Specimens
Place four drops of mixed specimen in a clean tube. Rinse a Pasteur pipette with 3% glacial acetic acid, draining thoroughly, and draw the four drops of CSF into the rinsed pipette. Allow the pipette to sit for 1 minute, mix the solution in the pipette, discard the first drop, and load the hemocytometer.
Cytocentrifugation Process
- Fluid added to conical chamber
- Specimen is centrifuged
- Cells present in the fluid are forced into a monolayer
- Fluid is absorbed by the filter paper blotter, producing a more concentrated area of cells.
- Albumin is used to help preserve cells and aid sticking to the slide
Pleocytosis
Increased numbers of normal cells; Lymphocytes, Monocytes
Cell type and Menigitis Cause Correlation
- A high number of neutrophils is indicates bacterial meningitis.
- A moderately elevated CSF WBC count with a high percentage of lymphocytes and monocytes suggests meningitis of viral, tubercular, fungal, or parasitic origin.
- Increased lymphocytes are also seen in both asymptomatic HIV infection and AIDS.
- A moderately elevated WBC count (less than 50 WBCs/µ L) with increased normal and reactive lymphocytes and plasma cells may indicate multiple sclerosis or other degenerative neurologic disorders.
nRBCs in CSF Specimen
NRBCs are seen as a result of bone marrow contamination during the spinal tap
Hemorrhagic Findings in CSF
- Increased macrophages indicates a previous hemorrhage
- Degradation of the phagocytized RBCs causes dark blue or black iron-containing hemosiderin granules
- Yellow hematoidin crystals represent further degeneration; iron-free, consisting of hemoglobin and unconjugated bilirubin
Choroidal Cells Appearance
Epithelial lining of the choroid plexus.
Seen singularly and in clumps.
Nucleoli are usually absent and nuclei have a uniform appearance
Ependymal Cells Appearance
From the lining of the ventricles and neural canal.
They have less defined cell membranes and are frequently seen in clusters.
Nucleoli are often present
Spindle-shaped Cells
Represent lining cells from the arachnoid.
They are usually seen in clusters and may be seen with systemic malignancies
Primary CNS Tumor Cells
Astrocytomas, retinoblastomas, and medulloblastomas
Usually appear in clusters and must be distinguished from normal clusters of ependymal, choroid plexus, lymphoma, and leukemia cells.
Fusing of cell walls, nuclear irregularities, and hyperchromatic nucleoli are seen in clusters of malignant cells.
CSF Chemical Test Reference Values
- Reference values for total CSF protein are 15 to 45 mg/dL, but are somewhat method dependent, and higher values are found in infants and people over age 40
- Abnormal values result from alterations in the permeability of the blood–brain barrier or increased production or metabolism by the neural cells in response to a pathologic condition.
Normal Protein Components of CSF
- Prealbumin is the second most prevalent fraction in CSF.
- Haptoglobin and ceruloplasmin (alpha globulins).
- Transferrin (beta globulin)
- Primarily IgG, a small amount IgA (gamma globulins)
- A separate carbohydrate-deficient transferrin fraction, “tau,” is seen in CSF and not in serum.
CSF Protein Levels and Implications
Low values: fluid is leaking from the CNS
High values: damage to the blood–brain barrier (most commonly meningitis and hemorrhage conditions), Ig production in CNS, decreased normal protein clearance from the fluid, and neural tissue degeneration
IgG Production Verification
Comparisons between serum and CSF levels of Albumin and IgG are done to determine whether IgG is increased from being produced within the CNS or is elevated as the result of a defect in the blood–brain barrier
CSF Protein Electrophoresis
- To detect oligoclonal bands, which represent inflammation within the CNS
- Two or more oligoclonal bands in the CSF that are not present in serum can help diagnose: multiple sclerosis
- Other abnormal banding patterns (not in serum): encephalitis, neurosyphilis, Guillain-Barré syndrome, and neoplastic disorders
- Use CSF immunofixation electrophoresis (IFE) and isoelectric focusing followed by silver staining
Myelin Basic Protein in CSF
- Myelin basic protein (MBP) in CSF indicates recent destruction of the myelin sheath that protects the axons of the neurons (demyelination).
- Can be used to monitor Multiple Sclerosis
CSF Glucose Values in Infection
- A markedly decreased CSF glucose level accompanied by an increased WBC count and a large percentage of neutrophils indicates bacterial meningitis.
- If the WBCs are mostly lymphocytes, tubercular meningitis is suspected.
- A normal CSF glucose value is found with an increased number of lymphocytes, the diagnosis would favor viral meningitis.
Non-Infectious Causes of Changes in CSF Glucose
Primarily by alterations in the mechanisms of glucose transport across the blood–brain barrier and by increased use of glucose by the brain cells
CSF Lactate
- Tool for diagnosing and managing meningitis cases.
- In bacterial, tubercular, and fungal meningitis, CSF lactate levels >25 mg/dL occur more consistently than decreased glucose
- Levels >35 mg/dL are seen with bacterial meningitis, whereas in viral meningitis, lactate levels remain <25 mg/dL.
- However, elevated CSF lactate can result from any condition that decreases oxygen flow to the tissues, not just meningitis
- RBCs contain lactate, and may cause a false positive/elevated result
Glutamine
Produced from ammonia and α-ketoglutarate by the brain cells.
Serves to remove toxic ammonia from the CNS
CSF Reference Range: 8 to 18 mg/dL
Elevated levels are associated with liver disorders that result in increased ammonia, and 75% of children with Reye’s syndrome have elevated CSF levels
Agents of Infectious Meningitis
- Streptococcus pneumoniae
- Haemophilus influenzae
- Escherichia coli
- Neisseria meningitidis
In newborns:
- Streptococcus agalactiae
- Listeria monocytogenes
Cryptococcal Meningitis
- Frequently occurring complication of AIDS
- Gram stain may show classic starburst pattern produced by Cryptococcus, seen more often than a positive India ink
- Latex agglutination tests to detect C. neoformans antigen in serum and CSF provide a more sensitive method than the India ink preparation, but can give false positives if Rheumatoid Factor is present
