Leukaemias and cytochemistry

19 Kerala MSc MLT Entrance practice questions on Leukaemias and cytochemistry, part of Haematology and Blood Banking. The first 19 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 · Medium

   A 45-year-old man has WBC 85,000/µL with neutrophils, myelocytes and metamyelocytes on the film. Which finding favours chronic myeloid leukaemia over a leukaemoid reaction?

   1. AA low LAP (NAP) score
   2. BNo increase in basophils
   3. CA high LAP (NAP) score
   4. DToxic granules and Döhle bodies

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   Answer: A · A low LAP (NAP) score

   Neutrophils in chronic-phase CML have little alkaline phosphatase, so the LAP score (100 neutrophils graded 0 to 4+) is low, whereas the neutrophils of a leukaemoid reaction to infection score high. Basophilia and eosinophilia also favour CML, while toxic granulation and Döhle bodies point to infection. The definitive test is BCR::ABL1 by PCR or FISH, or the Philadelphia chromosome on karyotype. The LAP score is also raised in polycythaemia vera and pregnancy, and low in PNH.

   • B: CML usually shows basophilia, so its absence favours a reactive cause.
   • C: A high LAP score is typical of a leukaemoid reaction.
   • D: Toxic granulation and Döhle bodies indicate infection or inflammation.

2. Question 2 · Easy

   By the FAB criterion, acute myeloid leukaemia is separated from acute lymphoblastic leukaemia when myeloperoxidase is positive in at least:

   1. A10% of the blasts
   2. B20% of the blasts
   3. C30% of the blasts
   4. D3% of the blasts

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   Answer: D · 3% of the blasts

   MPO (or Sudan black B) positivity in 3% or more of blasts indicates myeloid lineage, because lymphoblasts lack primary granules and are MPO negative. The 20% and 30% figures are the WHO and FAB blast thresholds for diagnosing acute leukaemia, not cytochemical cut-offs. An MPO-negative leukaemia is not automatically ALL: minimally differentiated AML and monoblastic leukaemia can be MPO negative, so flow cytometry is needed. Auer rods are strongly MPO positive.

   • A: A 10% cut-off is not used and would miss AML with few positive blasts.
   • B: 20% is the WHO blast threshold for acute leukaemia, not the MPO cut-off.
   • C: 30% was the FAB blast threshold for acute leukaemia, not the MPO cut-off.

3. Question 3 · Medium

   Naphthol AS-D chloroacetate esterase (the 'specific' esterase) is characteristically positive in:

   1. ANeutrophils and their precursors
   2. BMegaloblastic erythroblasts
   3. CMonocytes and their precursors
   4. DLymphoblasts of ALL

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   Answer: A · Neutrophils and their precursors

   Chloroacetate esterase is found in the granules of the neutrophil series from the promyelocyte stage on, and in mast cells, so it marks granulocytic differentiation. Monocytes are positive for the non-specific esterases (alpha-naphthyl acetate or butyrate), a reaction inhibited by sodium fluoride. Staining both esterases on one slide helps identify myelomonocytic leukaemia. Chloroacetate esterase also works on paraffin sections, which helps in diagnosing myeloid sarcoma.

   • B: Erythroblasts are negative for chloroacetate esterase.
   • C: Monocytes are positive for non-specific esterase, not chloroacetate esterase.
   • D: Lymphoblasts lack granule esterases and are negative.

4. Question 4 · Medium

   Sudan black B is often preferred to the MPO stain on blood films that are several weeks old. Why?

   1. AIt detects a peroxidase that resists storage
   2. BIt needs no fixation of the smear
   3. CIt stains granule lipid, which stays stable
   4. DIt stains glycogen, which never fades

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   Answer: C · It stains granule lipid, which stays stable

   Sudan black B is a lipophilic dye that dissolves in the phospholipids of granule membranes in neutrophils and, more weakly, monocytes. Its pattern closely follows MPO, but lipid does not lose activity on storage the way an enzyme does, so older smears still give reliable results. Its drawback is lower specificity, since a few ALL cases stain faintly. MPO itself is an enzyme reaction with hydrogen peroxide and a chromogen, and its activity declines as the smear ages.

   • A: Sudan black B is a fat stain, not an enzyme reaction.
   • B: The smear is fixed in formalin vapour before Sudan black B staining.
   • D: Glycogen is shown by the PAS stain, not Sudan black B.

5. Question 5 · Hard

   A 4-year-old girl has fever, pallor and bone pain. WBC 36,000/µL with 78% small blasts that have scanty agranular cytoplasm. Cytochemistry: MPO positive in under 3% of blasts, Sudan black B negative, non-specific esterase negative, PAS positive in coarse blocks. The most likely diagnosis is:

   1. AAcute promyelocytic leukaemia
   2. BAcute monoblastic leukaemia
   3. CAcute lymphoblastic leukaemia
   4. DAML with maturation

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   Answer: C · Acute lymphoblastic leukaemia

   Blasts negative for MPO and Sudan black B (under 3% positive) are not granulocytic, and a negative non-specific esterase argues against monoblasts. Coarse block positivity with PAS reflects glycogen in lymphoblasts and is typical of ALL, the commonest leukaemia of childhood. Promyelocytic leukaemia and AML with maturation are strongly MPO positive. Flow cytometry (CD19, CD10, cytoplasmic CD79a or CD3, TdT) then confirms the lineage and the B or T type.

   • A: Promyelocytic leukaemia cells are strongly MPO and Sudan black B positive.
   • B: Monoblasts are positive for non-specific esterase, which fluoride inhibits.
   • D: AML with maturation has many MPO-positive blasts and maturing granulocytes.

6. Question 6 · Hard

   A 32-year-old woman has gum bleeding and bruises. Hb 8.1 g/dL, WBC 2,900/µL, platelets 22,000/µL; PT 19 s (control 13 s), fibrinogen 90 mg/dL (200-400), D-dimer markedly raised. The marrow is full of heavily granular promyelocytes, some with bundles of Auer rods. Which genetic finding confirms the diagnosis?

   1. ARUNX1::RUNX1T1 from t(8;21)
   2. BPML::RARA from t(15;17)
   3. CBCR::ABL1 from t(9;22)
   4. DCBFB::MYH11 from inv(16)

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7. Question 7 · Easy

   Auer rods seen in the blasts of acute myeloid leukaemia are made of:

   1. AFused primary (azurophilic) granules
   2. BRemnants of the endoplasmic reticulum
   3. CAggregates of denatured haemoglobin
   4. DCondensed fragments of nuclear chromatin

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8. Question 8 · Hard

   A 66-year-old man has WBC 58,000/µL with 88% small mature lymphocytes, Hb 12.6 g/dL and platelets 1.9 lakhs/µL. Flow cytometry of the lymphocytes: CD19+, CD5+, CD23+, CD200+, FMC7 negative, weak surface kappa light chain only. The most likely diagnosis is:

   1. AChronic lymphocytic leukaemia
   2. BHairy cell leukaemia
   3. CPrecursor B-lymphoblastic leukaemia
   4. DMantle cell lymphoma in leukaemic phase

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9. Question 9 · Medium

   A high leucocyte (neutrophil) alkaline phosphatase score is expected in which condition?

   1. AParoxysmal nocturnal haemoglobinuria
   2. BChronic myeloid leukaemia, chronic phase
   3. CPolycythaemia vera
   4. DHypophosphatasia

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10. Question 10 · Medium

    Nuclear staining for TdT in the blasts of an acute leukaemia shows that the cells are:

    1. AMature, surface Ig-bearing B cells
    2. BAbnormal plasma cells in myeloma
    3. CImmature (precursor) lymphoid cells
    4. DCells of the monocyte lineage

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11. Question 11 · Easy

    An elderly man has a lymphocytosis of small mature-looking lymphocytes, and the film shows many smudge (basket) cells. This picture suggests:

    1. AInfectious mononucleosis
    2. BChronic myeloid leukaemia
    3. CChronic lymphocytic leukaemia
    4. DAcute lymphoblastic leukaemia

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12. Question 12 · Hard

    A 2-year-old child with Down syndrome has pancytopenia and a dry tap; a trephine shows marrow fibrosis. The blasts, some with cytoplasmic blebs, are MPO negative, Sudan black B negative and non-specific esterase negative. Which test best establishes their lineage?

    1. ATRAP staining of the blasts
    2. BCytoplasmic CD3 by flow cytometry
    3. CPAS stain for glycogen blocks
    4. DFlow cytometry for CD41 and CD61

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13. Question 13 · Medium

    In the cytochemical myeloperoxidase stain, the enzyme oxidises the chromogen (for example diaminobenzidine) using:

    1. ANaphthol AS-D chloroacetate
    2. BHydrogen peroxide
    3. CPeriodic acid
    4. DAlpha-naphthyl acetate

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14. Question 14 · Medium

    Mononuclear cells with fine cytoplasmic projections show tartrate-resistant acid phosphatase (TRAP) activity. This finding supports:

    1. AAcute monoblastic leukaemia
    2. BHairy cell leukaemia
    3. CChronic lymphocytic leukaemia
    4. DSézary syndrome

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15. Question 15 · Hard

    A 52-year-old woman has 46% blasts in the marrow. On a double esterase stain, about 35% of the leukaemic cells are positive for chloroacetate esterase and about 30% show diffuse alpha-naphthyl acetate esterase that sodium fluoride abolishes. MPO is positive in 40% of blasts. The most likely diagnosis is:

    1. AAcute lymphoblastic leukaemia
    2. BAcute monoblastic leukaemia
    3. CAML with maturation (granulocytic only)
    4. DAcute myelomonocytic leukaemia

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16. Question 16 · Hard

    For an LAP score, 100 neutrophils are graded 0 to 4+: 20 cells score 0, 30 score 1+, 25 score 2+, 15 score 3+ and 10 score 4+. The laboratory's reference range is 20-100. What is the score and its meaning in a patient with WBC 52,000/µL?

    1. A165; favours chronic myeloid leukaemia
    2. B33; favours chronic myeloid leukaemia
    3. C80; lies within the reference range
    4. D165; favours a leukaemoid reaction

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17. Question 17 · Easy

    In the FAB scheme, L3 lymphoblasts with deeply basophilic cytoplasm and prominent vacuoles correspond to:

    1. AMature B-cell (Burkitt-type) leukaemia
    2. BChildhood common precursor B-cell ALL
    3. CPrecursor T-cell lymphoblastic leukaemia
    4. DAcute megakaryoblastic leukaemia

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18. Question 18 · Medium

    Blasts stain strongly with alpha-naphthyl acetate esterase, and the reaction disappears when sodium fluoride is added. These blasts are most likely:

    1. AMyeloblasts
    2. BMonoblasts
    3. CProerythroblasts
    4. DLymphoblasts

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19. Question 19 · Easy

    Gum hypertrophy and skin infiltration at diagnosis are most typical of which type of acute leukaemia?

    1. AAcute monocytic (monoblastic) leukaemia
    2. BAcute lymphoblastic leukaemia
    3. CAcute erythroid leukaemia
    4. DAcute promyelocytic leukaemia

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