CSF analysis

12 ASCP MLS practice questions on CSF analysis, part of Urinalysis and Body Fluids. The first 12 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 29-year-old man has had headache, neck stiffness and burning pains in his legs for 6 days. Two weeks ago he returned from Hawaii, where he ate unwashed garden salad and, on a dare, a raw snail. CSF: opening pressure raised; WBC 480/µL [480 x 10^6/L]; Wright-stained cytocentrifuge differential 40% eosinophils, 45% lymphocytes, 15% monocytes; glucose 54 mg/dL [3.0 mmol/L] with plasma glucose 92 mg/dL [5.1 mmol/L]; protein 82 mg/dL [820 mg/L]. Gram stain and cryptococcal antigen are negative. Which organism is the most likely cause?

   1. AMycobacterium tuberculosis
   2. BNaegleria fowleri
   3. CCryptococcus neoformans
   4. DAngiostrongylus cantonensis

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   Answer: D · Angiostrongylus cantonensis

   Eosinophils making up 10% or more of the CSF white cells (or at least 10/µL) define eosinophilic meningitis, and they are identified on a stained cytocentrifuge smear rather than in the counting chamber. The most common infectious cause worldwide is Angiostrongylus cantonensis, the rat lungworm, acquired by eating raw snails or slugs, or produce contaminated by them, in Hawaii, Southeast Asia and the Pacific. The larvae migrate to the meninges and brain, causing headache and painful paresthesias, with moderately raised protein and a normal or slightly low glucose. Here the CSF-to-plasma glucose ratio is about 0.59, which is normal. The diagnosis rests on the exposure history and the CSF eosinophilia, and it can be supported by PCR of the CSF.

   • A: Tuberculous meningitis gives a lymphocytic CSF with low glucose and high protein, not eosinophils.
   • B: Naegleria causes a rapidly fatal neutrophilic meningoencephalitis with low glucose after freshwater swimming.
   • C: Cryptococcal antigen is negative, and cryptococcal meningitis gives a lymphocytic CSF with low glucose.

2. Question 2 · Medium

   The CSF tubes shown were filled in order at one lumbar puncture, each labeled with its red cell count. The pattern most likely indicates:

   

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   1. ASubarachnoid hemorrhage
   2. BBlood from a traumatic tap
   3. CBacterial meningitis
   4. DAn old intracranial bleed

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   Answer: B · Blood from a traumatic tap

   The red cell count falls from 8,600/µL [8,600 x 10^6/L] in tube 1 to 180/µL [180 x 10^6/L] in tube 3, so the blood is clearing as the fluid is collected. That is the pattern of blood introduced by the needle. In a subarachnoid hemorrhage the blood is spread evenly through all the tubes, and the supernatant becomes xanthochromic within hours. Clots in the first tube also point to a traumatic tap, and the cell count should be done on the last tube.

   • A: A subarachnoid bleed gives evenly bloody fluid in every tube.
   • C: Meningitis raises white cells and makes CSF cloudy, not bloody tube by tube.
   • D: Blood from an older bleed is evenly mixed and gives a xanthochromic supernatant.

3. Question 3 · Medium

   CSF shows many neutrophils, a low glucose and a high protein. What is the most likely diagnosis?

   1. AA normal CSF
   2. BTuberculous meningitis
   3. CBacterial meningitis
   4. DViral meningitis

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   Answer: C · Bacterial meningitis

   Bacterial meningitis typically gives a high neutrophil count, glucose below about two-thirds of the plasma level, and raised protein. Bacteria use glucose and damage the blood-brain barrier. Gram stain and culture identify the organism, and antigen or PCR panels help. It is a medical emergency.

   • A: Normal CSF has very few cells and no neutrophils.
   • B: Tuberculous meningitis gives lymphocytes, low glucose and high protein, often with a fibrin web.
   • D: Viral meningitis gives lymphocytes with a normal glucose.

4. Question 4 · Medium

   CSF results: WBC 180/µL [180 × 10^6/L] with 85% lymphocytes; glucose 62 mg/dL [3.4 mmol/L] with a normal plasma glucose; protein 70 mg/dL [700 mg/L]; Gram stain negative. The most likely cause is:

   1. ATuberculous meningitis
   2. BCryptococcal meningitis
   3. CViral (aseptic) meningitis
   4. DBacterial meningitis

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   Answer: C · Viral (aseptic) meningitis

   A moderate rise in white cells that are mostly lymphocytes, with a normal glucose and a mildly raised protein, is the typical viral (aseptic) meningitis pattern. Viruses do not consume glucose, so CSF glucose stays normal. Tuberculous and fungal meningitis also give lymphocytes but usually lower the glucose and raise the protein further. Very early viral meningitis can show neutrophils, so a repeat tap may show the shift to lymphocytes.

   • A: Tuberculous meningitis usually lowers glucose and raises protein markedly.
   • B: Cryptococcal meningitis usually lowers glucose and is confirmed by cryptococcal antigen.
   • D: Bacterial meningitis gives mostly neutrophils and a low glucose.

5. Question 5 · Medium

   All three CSF tubes are equally bloody, and the supernatant is yellow after centrifugation. These findings most suggest:

   1. AA traumatic lumbar puncture
   2. BMultiple sclerosis
   3. CBacterial meningitis
   4. DSubarachnoid hemorrhage

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   Answer: D · Subarachnoid hemorrhage

   In a traumatic tap the blood is heaviest in tube 1 and clears in later tubes, and the supernatant is clear when the fluid is spun promptly. Even blood across the tubes with a yellow (xanthochromic) supernatant means the blood was in the CSF before the tap, as in subarachnoid hemorrhage. Xanthochromia comes from red cell breakdown products, first oxyhemoglobin and then bilirubin, and appears a few hours after the bleed. Macrophages containing red cells or hemosiderin also point to an earlier bleed.

   • A: A traumatic tap shows more blood in tube 1 than in later tubes and a clear supernatant.
   • B: Multiple sclerosis gives a clear fluid with oligoclonal bands, not blood.
   • C: Bacterial meningitis gives a cloudy fluid with neutrophils, not evenly bloody tubes.

6. Question 6 · Hard

   A 38-year-old man has had headache and fever for 3 weeks. CSF: WBC 260/µL [260 × 10^6/L], 80% lymphocytes; glucose 22 mg/dL [1.2 mmol/L] with plasma glucose 100 mg/dL [5.6 mmol/L]; protein 310 mg/dL [3,100 mg/L]. A fine, web-like clot forms in the tube kept overnight in the refrigerator, and cryptococcal antigen is negative. The most likely cause is:

   1. ATuberculous meningitis
   2. BEnteroviral meningitis
   3. CPartially treated bacterial meningitis
   4. DCryptococcal meningitis

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7. Question 7 · Hard

   A 62-year-old with poorly controlled diabetes has fever and neck stiffness. CSF: WBC 1,800/µL [1,800 × 10^6/L], 90% neutrophils; glucose 68 mg/dL [3.8 mmol/L]; protein 240 mg/dL [2,400 mg/L]. Plasma glucose is 340 mg/dL [18.9 mmol/L]. How should the CSF glucose be interpreted?

   1. AUninterpretable until the patient has fasted for 8 hours
   2. BLow for the plasma level, fitting bacterial meningitis
   3. CHigh, because glucose leaks across an inflamed barrier
   4. DNormal, which makes bacterial meningitis unlikely

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8. Question 8 · Hard

   A traumatic tap gives CSF RBC 12,000/µL [12,000 × 10^6/L] and WBC 40/µL [40 × 10^6/L]. The blood RBC is 4.0 × 10^6/µL [4.0 × 10^12/L] and the blood WBC is 8.0 × 10^3/µL [8.0 × 10^9/L]. What is the CSF WBC count corrected for the added blood?

   1. A40/µL
   2. B64/µL
   3. C24/µL
   4. D16/µL

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9. Question 9 · Hard

   Clear CSF is diluted 1:2 with dilute acetic acid and loaded into a Neubauer hemocytometer. A total of 45 white cells are counted in the 9 large squares of one side. What is the WBC count?

   1. A900/µL
   2. B100/µL
   3. C50/µL
   4. D10/µL

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10. Question 10 · Easy

    Normal CSF glucose is about what percentage of the plasma glucose?

    1. AAbout 20-30%
    2. BAbout 60-70%
    3. CAbout 100%
    4. DAbout 120%

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11. Question 11 · Easy

    The CSF cell count is usually performed on the last tube collected because that tube:

    1. AHas the least blood from the tap
    2. BHolds the most cells for counting
    3. CMust stay sterile for culture
    4. DHas the lowest protein for chemistry

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12. Question 12 · Medium

    Isoelectric focusing shows oligoclonal IgG bands in the CSF that are absent from the patient's serum. What does this indicate?

    1. AA monoclonal gammopathy such as myeloma
    2. BIgG leaking in through a damaged blood-brain barrier
    3. CBlood contamination from a traumatic tap
    4. DIgG produced within the central nervous system

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