Cerebrospinal fluid

16 DOH Abu Dhabi (HAAD) lab licensing practice questions on Cerebrospinal fluid, part of Urinalysis and Body Fluids. The first 16 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 19-year-old student has fever, a petechial rash and neck stiffness. A lumbar puncture is done at 01:00, before any antibiotic, and ceftriaxone is started straight afterwards. The night porter puts the CSF tubes in a refrigerator at 4 °C, and they reach the laboratory at 08:00. CSF: WBC 2,800 x 10^6/L, 90% neutrophils; glucose 0.9 mmol/L (16 mg/dL) with plasma glucose 6.2 mmol/L (112 mg/dL); protein 3.1 g/L (310 mg/dL). The Gram stain shows intracellular gram-negative diplococci, confirmed by a second reader. Blood and chocolate agar plates, whose QC with a Neisseria meningitidis strain passed, show no growth after 72 hours in CO2. What best explains the negative culture?

   1. AA Gram stain artifact, not real bacteria
   2. BCold storage killed the meningococci
   3. CMedia unable to support Neisseria growth
   4. DAntibiotics given before the lumbar puncture

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   Answer: B · Cold storage killed the meningococci

   Neisseria meningitidis and Haemophilus influenzae are fragile and lose viability quickly in the cold, so CSF for bacterial culture is kept at room temperature (or at 35-37 °C) and plated as soon as possible; only CSF for virus testing may be refrigerated. Here the CSF was taken before any antibiotic, the plates passed QC with a meningococcal strain, and a purulent CSF with a very low glucose and gram-negative diplococci confirmed by a second reader is not an artifact. The 7 hours at 4 °C is therefore the most likely reason. The laboratory should report the Gram stain, record the storage problem and suggest meningococcal PCR on the CSF, which does not need live organisms.

   • A: A second reader confirmed the organisms, and the cell count and glucose fit bacterial meningitis.
   • C: Both plates passed QC with a Neisseria meningitidis strain.
   • D: The lumbar puncture was done before the first dose of ceftriaxone.

2. Question 2 · Hard

   A 36-year-old man developed tingling feet and then weakness rising to his thighs and arms over 8 days; his tendon reflexes are absent. Three weeks ago he had diarrhea after eating undercooked chicken. Lumbar puncture gives clear, colorless CSF in all tubes: WBC 3 x 10^6/L (reference 0-5 x 10^6/L), RBC 0; protein 1.85 g/L (185 mg/dL; reference 0.15-0.45 g/L); glucose 3.6 mmol/L (65 mg/dL) with plasma glucose 5.8 mmol/L (104 mg/dL); Gram stain negative. The CSF findings are most consistent with:

   1. AA traumatic lumbar puncture
   2. BMultiple sclerosis
   3. CViral meningitis
   4. DGuillain-Barré syndrome

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   Answer: D · Guillain-Barré syndrome

   A raised CSF protein with a normal cell count (albuminocytologic dissociation) in a patient with ascending weakness and absent reflexes is typical of Guillain-Barré syndrome. Inflammation of the nerve roots lets protein leak into the CSF without drawing in white cells, and the rise is most marked after the first week. Campylobacter jejuni enteritis, often from undercooked poultry, is a common trigger. Viral meningitis gives a lymphocytic pleocytosis, multiple sclerosis usually leaves the protein normal or slightly raised, and a traumatic tap is excluded because no red cells were found. A white cell count above about 50 x 10^6/L should prompt a search for another diagnosis.

   • A: No red cells were found, so blood did not add protein to the CSF.
   • B: Multiple sclerosis rarely raises CSF protein this much or causes rapid ascending weakness.
   • C: Viral meningitis raises the white cell count, which is normal here.

3. Question 3 · Medium

   The CSF tubes shown are numbered in the order of collection, with their red cell counts. After centrifugation every supernatant is clear and colorless. The red cells most likely come from:

   

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   1. AA traumatic lumbar puncture
   2. BA subarachnoid hemorrhage
   3. CHerpes simplex encephalitis
   4. DAn intracerebral hemorrhage

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   Answer: A · A traumatic lumbar puncture

   The red cell count falls steeply from tube 1 to tube 3, showing that blood entered at the needle and was washed out as the fluid flowed. In a subarachnoid hemorrhage the blood is mixed evenly through the CSF, so the counts stay about the same in every tube. A clear, colorless supernatant (no xanthochromia) also argues against bleeding that began hours before the tap. Contamination from a traumatic tap is one reason the cell count is done on the last tube collected.

   • B: Blood from a subarachnoid bleed is evenly mixed, giving similar counts in every tube and xanthochromia after a few hours.
   • C: Red cells from a hemorrhagic encephalitis are present evenly in all tubes, with a raised white cell count.
   • D: Blood that reaches the CSF from an intracerebral bleed is also evenly distributed rather than clearing tube by tube.

4. Question 4 · Easy

   The reference range for the white cell count in normal adult CSF is:

   1. A50-100 × 10^6/L (50-100/µL)
   2. B0-5 × 10^6/L (0-5/µL)
   3. C0-30 × 10^6/L (0-30/µL)
   4. D4-11 × 10^9/L (4,000-11,000/µL)

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   Answer: B · 0-5 × 10^6/L (0-5/µL)

   Normal adult CSF contains very few cells, 0 to 5 × 10^6/L, mostly lymphocytes and monocytes. Newborns have higher counts, up to about 30 × 10^6/L, with more monocytes. Any rise in an adult, or more than an occasional neutrophil, needs an explanation. Because the counts are so low, a hemocytometer or an analyzer validated for body fluids is used, and the differential is done on a cytocentrifuge slide.

   • A: Counts of 50-100 × 10^6/L are clearly raised in adults.
   • C: Up to 30 × 10^6/L is the upper range for newborns, not adults.
   • D: 4-11 × 10^9/L is the adult blood white cell count.

5. Question 5 · Hard

   A purulent CSF (WBC 3,000 × 10^6/L, mostly neutrophils, with gram-positive diplococci) has a glucose of 2.4 mmol/L (43 mg/dL) on arrival. The same tube, left at room temperature and retested 3 hours later with acceptable QC on both runs, gives 1.5 mmol/L (27 mg/dL). The best explanation is:

   1. AEvaporation concentrated the sample
   2. BLeukocytes and bacteria kept using glucose
   3. CGlucose bound to the high CSF protein
   4. DThe analyzer drifted between the runs

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   Answer: B · Leukocytes and bacteria kept using glucose

   Cells and bacteria in CSF continue glycolysis after collection, so glucose falls and lactate rises the longer the specimen waits. The effect is greatest in purulent fluid with many neutrophils and organisms, as here. CSF chemistry should be tested promptly, or the fluid separated from its cells and frozen, and read against a plasma glucose drawn shortly before the tap. The result on arrival is the one that reflects the patient.

   • A: Evaporation would raise the glucose, not lower it.
   • C: Protein does not bind glucose and hide it from the assay.
   • D: Acceptable QC on both runs makes analyzer drift unlikely.

6. Question 6 · Hard

   An 8-year-old has had fever and headache for 10 hours during an enterovirus outbreak. CSF: WBC 220 × 10^6/L, 65% neutrophils; glucose 3.6 mmol/L (65 mg/dL) with plasma glucose 5.4 mmol/L (97 mg/dL); protein 0.55 g/L (reference 0.15-0.45 g/L); lactate 2.0 mmol/L (reference 1.1-2.4 mmol/L); Gram stain negative. A repeat CSF 24 hours later shows 75% lymphocytes. The most likely diagnosis is:

   1. ATuberculous meningitis
   2. BBacterial meningitis, seen early
   3. CFungal meningitis
   4. DViral meningitis, seen early

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7. Question 7 · Hard

   A 30-year-old took oral amoxicillin for 2 days before admission with a 3-day history of fever and neck stiffness. CSF: WBC 650 × 10^6/L, 55% neutrophils; glucose 2.0 mmol/L (36 mg/dL) with plasma glucose 6.0 mmol/L (108 mg/dL); protein 1.6 g/L (160 mg/dL; reference 0.15-0.45 g/L); lactate 6.5 mmol/L (reference 1.1-2.4 mmol/L); Gram stain negative. The most likely diagnosis is:

   1. ATuberculous meningitis
   2. BCryptococcal (fungal) meningitis
   3. CPartially treated bacterial meningitis
   4. DViral (enteroviral) meningitis

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8. Question 8 · Hard

   After a skull fracture, a patient has clear fluid dripping from one nostril. The fluid is positive for glucose on a reagent strip. Which test best confirms that it is CSF?

   1. AQuantitative glucose
   2. BBeta-2 transferrin
   3. CTotal protein
   4. DLactate

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9. Question 9 · Medium

   Why does CSF glutamine rise in hepatic encephalopathy?

   1. AGlutamine leaks in through a damaged blood-brain barrier
   2. BThe failing liver releases glutamine into the blood
   3. CBacteria in the CSF produce glutamine
   4. DBrain cells convert excess ammonia to glutamine

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10. Question 10 · Easy

    A CSF cell count should be done within about an hour of collection because:

    1. ARed cells crenate and are counted as white cells
    2. BProtein precipitates and hides the cells
    3. CWhite cells keep dividing, so the count rises
    4. DWhite cells begin to lyse, so the count falls

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11. Question 11 · Hard

    A cytocentrifuge slide of ventricular CSF from a 2-year-old with a shunt shows a few tight clusters of cells with round, uniform nuclei, even chromatin and distinct cell borders. The cell count and glucose are normal. How should these cells be interpreted?

    1. ALeukemic blasts from a CNS relapse
    2. BMalignant cells from a medulloblastoma
    3. CMetastatic carcinoma cells
    4. DBenign choroid plexus or ependymal cells

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12. Question 12 · Hard

    Results: CSF IgG 80 mg/L (8.0 mg/dL), serum IgG 10 g/L (1,000 mg/dL), CSF albumin 200 mg/L (20 mg/dL), serum albumin 40 g/L (4.0 g/dL). The laboratory's upper limit for the IgG index is 0.70. What is the IgG index, and what does it suggest?

    1. A0.40; no IgG is being made within the CNS
    2. B1.6; IgG is being made within the CNS
    3. C0.63; no IgG is being made within the CNS
    4. D1.6; leakage across the blood-brain barrier

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13. Question 13 · Medium

    What does a raised CSF myelin basic protein most directly indicate?

    1. ABacterial infection of the meninges
    2. BActive breakdown of myelin
    3. CIgG synthesis within the brain
    4. DDamage to the blood-brain barrier

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14. Question 14 · Medium

    A drop of albumin is often added to a CSF with very few cells before a cytocentrifuge slide is made. The purpose is to:

    1. ALyse red cells that hide the white cells
    2. BRaise the cell yield and reduce cell distortion
    3. CStop the fluid from clotting in the chamber
    4. DStain the nuclei before the slide dries

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15. Question 15 · Medium

    CSF from a healthy premature newborn is pale yellow. No red cells are seen, and cranial ultrasound is normal. The most likely cause is:

    1. AAn immature blood-brain barrier
    2. BA recent subarachnoid hemorrhage
    3. CCarotene from the diet
    4. DA traumatic tap during collection

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16. Question 16 · Medium

    Isoelectric focusing shows identical oligoclonal IgG bands in the patient's CSF and serum, with no extra bands in the CSF. This pattern indicates:

    1. AIgG made within the CNS, as in multiple sclerosis
    2. BBands passed from the blood, not CNS synthesis
    3. CA technical fault, since serum never shows bands
    4. DA monoclonal protein from myeloma

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