MLT GlobeUrinalysis & Body Fluids: CSF – page 2
40 Urinalysis & Body Fluids MCQs on CSF with answers and explanations.
After head trauma, a patient has clear fluid dripping from the nose. Which laboratory test best confirms that the fluid is CSF?
Beta-2 transferrin is found in CSF and perilymph but not in nasal secretions or blood, making it a specific marker for CSF leak. Glucose dipsticks give false positives from nasal mucus or blood.
CSF arrives in the laboratory at night. How should the microbiology tube be stored if it cannot be processed immediately?
Microbiology CSF is kept at room temperature because fastidious organisms such as Neisseria meningitidis and Haemophilus influenzae die in the cold. Chemistry tubes may be frozen and hematology tubes refrigerated.
CSF protein electrophoresis shows several discrete bands in the gamma region that are absent from the patient's paired serum. This finding most supports:
Oligoclonal bands found in CSF but not serum show intrathecal IgG synthesis, as in multiple sclerosis. Bands present in both CSF and serum reflect systemic immune activity.
The CSF/serum albumin ratio (albumin index) is used mainly to assess:
Albumin is made only in the liver, so a raised CSF/serum albumin ratio shows leakage across the blood-brain barrier. Intrathecal IgG production is assessed by the IgG index.
A cytocentrifuge slide of CSF shows macrophages containing dark blue-black haemosiderin granules. This most suggests:
Siderophages form when macrophages break down red cells over about 2 days or more, indicating earlier subarachnoid haemorrhage. A traumatic tap is too recent to produce them.
Three tubes of bloody CSF are collected. The blood in tube 1 forms a clot on standing. This suggests:
Blood from a traumatic tap contains plasma fibrinogen and can clot, while blood from a subarachnoid haemorrhage has been defibrinated and does not. Clotting is also seen with very high protein, as in spinal block.
CSF from a patient with meningitis shows 25% eosinophils. The patient recently ate raw snails in Southeast Asia. The most likely cause is:
Eosinophilic meningitis suggests parasitic infection, especially the rat lungworm Angiostrongylus from raw snails or slugs. It is also seen with shunt reactions. Bacterial meningitis is neutrophilic.
Why is CSF for Gram stain concentrated by cytocentrifugation before staining?
Cytocentrifugation concentrates cells and bacteria onto a small area of the slide, detecting organisms at lower concentrations than a direct smear.
CSF is diluted 1:2 with diluting fluid. WBCs counted in the four large corner squares of a Neubauer chamber (each 1 mm² × 0.1 mm) total 36. The WBC count is:
Count × dilution ÷ volume counted = 36 × 2 ÷ (4 × 0.1 µL) = 180 cells/µL. Forgetting the dilution gives 90.
A patient with suspected neurosyphilis has a non-reactive CSF VDRL. Which statement is correct?
A reactive CSF VDRL (in a non-bloody sample) is diagnostic, but its sensitivity is limited, so a negative result does not rule out neurosyphilis. VDRL detects non-treponemal (cardiolipin) antibodies.
A patient with liver cirrhosis is confused and drowsy. Which CSF finding is most useful to support hepatic encephalopathy?
Ammonia detoxified in the brain forms glutamine, so CSF glutamine rises in hepatic encephalopathy. Low glucose and high lactate suggest bacterial meningitis.
CSF from an elderly adult with bacterial meningitis shows Gram-positive lancet-shaped diplococci. The most likely organism is:
Streptococcus pneumoniae is a Gram-positive lancet-shaped diplococcus and the commonest cause of bacterial meningitis in adults. N. meningitidis is Gram-negative and H. influenzae is a Gram-negative coccobacillus.
CSF from a 5-day-old baby with meningitis shows Gram-positive cocci in chains. Which organism is most likely?
Group B streptococcus (S. agalactiae), acquired from the mother's genital tract, is a leading cause of neonatal meningitis and appears as Gram-positive cocci in chains.
A patient with ascending weakness a few weeks after a diarrheal illness has CSF with markedly raised protein but a normal cell count. This pattern suggests:
High CSF protein with a normal white count (albuminocytologic dissociation) is typical of Guillain–Barré syndrome. Meningitis gives raised white cells.
A premature neonate has yellow (xanthochromic) CSF with a normal cell count and no signs of hemorrhage. The most likely explanation is:
Neonates, especially premature ones, have a more permeable blood–brain barrier and often high bilirubin, giving xanthochromia without bleeding. A traumatic tap gives red, not yellow, fluid initially.
Which CSF chemistry finding best helps separate bacterial from viral meningitis, especially after antibiotics are started?
CSF lactate rises markedly in bacterial meningitis due to anaerobic metabolism and neutrophils, and stays high for a time after antibiotics. It is usually normal or slightly raised in viral meningitis.
Undiluted CSF is counted in a Neubauer hemocytometer. A total of 45 WBCs is counted in all 9 large squares (each 1 mm² × 0.1 mm deep). The WBC count is:
Volume counted = 9 × 0.1 µL = 0.9 µL. Cells/µL = 45 ÷ 0.9 × dilution factor 1 = 50 cells/µL.
A traumatic tap gives CSF RBC 7000/µL and WBC 30/µL. Blood counts are normal. Using the correction of 1 WBC per 700 RBC, the corrected CSF WBC is:
Blood-derived WBCs = 7000 ÷ 700 = 10/µL; corrected WBC = 30 − 10 = 20/µL. This simple correction applies only when the peripheral blood count is normal.
A CSF cytospin from a patient with a ventricular shunt shows tight clusters of cells with round nuclei and abundant cytoplasm, looking uniform. They most likely are:
Choroid plexus and ependymal cells can appear in clusters after shunts or neurosurgery and have uniform nuclei. They must not be mistaken for malignant cells, which show pleomorphism.
A 65-year-old has rapidly progressive dementia and myoclonus. Which CSF test is the most specific for sporadic Creutzfeldt-Jakob disease?
RT-QuIC detects the seeding activity of the abnormal prion protein and has very high specificity. The 14-3-3 protein is a marker of rapid neuronal damage and is less specific.