Blood from a 63-year-old man with a lymphocyte count of 9.8 × 10^9/L is studied by flow cytometry. Within the lymphocyte gate, 82% of events are CD19+, CD5+, CD23+ B cells with dim kappa, 13% are CD3+ T cells, and 5% form a discrete cluster positive for both CD3 and CD19. Single-stained compensation controls run today are correct. On a plot of forward scatter area against forward scatter height, the double-positive events lie off the main diagonal, with an area about twice that expected for their height. The best explanation is:

Doublets of T and B cells; apply a singlet gate

A second, biphenotypic T/B lymphoid neoplasm

Nonspecific antibody binding to Fc receptors

Fluorochrome spillover from incorrect compensation

Blood from a patient with lymphocytosis is stained for surface light chains, and the plot shows the CD19-positive B cells. What does it show?

A monoclonal, kappa-restricted B-cell population

A monoclonal, lambda-restricted B-cell population

B cells that have lost surface light chains

A polyclonal B-cell population with a normal ratio

Marrow aspirate smears show no spicules and a cell mix like blood: mostly neutrophils and lymphocytes, with very few erythroid precursors or myelocytes. The trephine taken at the same time is 50% cellular with normal maturation and no fibrosis on reticulin stain. What best explains the aspirate findings?

Dilution of the aspirate with blood

Aplastic anemia with fatty marrow

Marrow fibrosis causing a poor tap

Clotting of the aspirate sample

After chemotherapy for B-lymphoblastic leukemia, a 6-year-old's regenerating marrow has 12% CD19-positive, CD10-positive cells. They form a smooth spectrum from CD34-positive, CD20-negative cells to CD20-positive mature B cells, with no aberrant markers. The most likely interpretation is:

Normal B-cell precursors (hematogones)

Relapse of B-lymphoblastic leukemia

Mature B-cell lymphoma in the marrow

Flow cytometry and bone marrow examination

12 DOH Abu Dhabi (HAAD) lab licensing practice questions on Flow cytometry and bone marrow examination, part of Hematology. 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.

Question 1 · Hard
Blood from a 63-year-old man with a lymphocyte count of 9.8 × 10^9/L is studied by flow cytometry. Within the lymphocyte gate, 82% of events are CD19+, CD5+, CD23+ B cells with dim kappa, 13% are CD3+ T cells, and 5% form a discrete cluster positive for both CD3 and CD19. Single-stained compensation controls run today are correct. On a plot of forward scatter area against forward scatter height, the double-positive events lie off the main diagonal, with an area about twice that expected for their height. The best explanation is:
1. AA second, biphenotypic T/B lymphoid neoplasm
2. BNonspecific antibody binding to Fc receptors
3. CDoublets of T and B cells; apply a singlet gate
4. DFluorochrome spillover from incorrect compensation
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Answer: C · Doublets of T and B cells; apply a singlet gate
Two cells stuck together pass the laser as one event and carry the markers of both, so a T cell and a B cell together appear CD3+ CD19+. A doublet gives a longer pulse, so its forward scatter area is high for its height and it falls off the singlet diagonal; gating on singlets (FSC-A against FSC-H or width) removes these events. True biphenotypic T/B neoplasms are exceptionally rare, and these events have doublet scatter. Compensation errors skew a whole population rather than creating a separate cluster, and today's compensation controls are correct. Fc receptor binding gives broad false positivity, mainly on monocytes and B cells, and does not double the scatter pulse area.
- A: Biphenotypic T/B neoplasms are exceptionally rare; these events have doublet scatter.
- B: Fc binding does not double the forward scatter area of the events.
- D: Compensation controls are correct, and spillover does not form a separate cluster.
Question 2 · Medium
Blood from a patient with lymphocytosis is stained for surface light chains, and the plot shows the CD19-positive B cells. What does it show?
Figure: MedExams
1. AA monoclonal, kappa-restricted B-cell population
2. BA monoclonal, lambda-restricted B-cell population
3. CB cells that have lost surface light chains
4. DA polyclonal B-cell population with a normal ratio
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Answer: A · A monoclonal, kappa-restricted B-cell population
Each B cell makes only one light chain, and a normal (polyclonal) B-cell population has a mixture, with a kappa to lambda ratio of roughly 0.5 to 3. Here 94% of the B cells carry kappa and only 3% carry lambda, a ratio of about 30 to 1. Such light-chain restriction is the flow cytometry marker of a clonal B-cell population, as in chronic lymphocytic leukemia or another B-cell lymphoma. The clone is then characterized with markers such as CD5, CD10 and CD23.
- B: Lambda-positive cells, in the upper left quadrant, are only 3%.
- C: Light-chain-negative cells, in the lower left quadrant, are only 2.5%.
- D: A polyclonal population would show both kappa and lambda cells in a ratio near 2 to 1.
Question 3 · Medium
Bone marrow from a patient with pancytopenia is analyzed by flow cytometry, plotting CD45 against side scatter. The population in gate R1, 62% of all events, is most likely made up of:
Figure: MedExams
1. ABlasts
2. BNucleated red cells
3. CMature lymphocytes
4. DMonocytes
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Answer: A · Blasts
On a CD45 versus side scatter plot each cell type has its own place. Gate R1 holds cells with dim CD45 and low side scatter, the classic position of blasts, which have less CD45 than mature leukocytes and few granules. Mature lymphocytes sit further right with bright CD45, monocytes are bright with moderate side scatter, and granulocytes have high side scatter. A large dim-CD45 population in a pancytopenic marrow suggests acute leukemia, which is then typed with lineage markers.
- B: Nucleated red cells are CD45-negative, at the far left of the plot.
- C: Mature lymphocytes have bright CD45, to the right of R1.
- D: Monocytes have bright CD45 and moderate side scatter.
Question 4 · Hard
Marrow aspirate smears show no spicules and a cell mix like blood: mostly neutrophils and lymphocytes, with very few erythroid precursors or myelocytes. The trephine taken at the same time is 50% cellular with normal maturation and no fibrosis on reticulin stain. What best explains the aspirate findings?
1. ADilution of the aspirate with blood
2. BAplastic anemia with fatty marrow
3. CMarrow fibrosis causing a poor tap
4. DClotting of the aspirate sample
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Answer: A · Dilution of the aspirate with blood
Marrow spicules carry the hematopoietic cells, and a smear without them that looks like blood has been diluted. This happens when too much is drawn in one pull, because blood floods in after the first few tenths of a millilitre. The normal trephine rules out aplasia and fibrosis. The first small pull should go to the smears, with a separate pull for flow cytometry or other tests.
- B: The trephine is 50% cellular, so the marrow is not aplastic.
- C: The reticulin stain shows no fibrosis, so the poor smear is not from fibrosis.
- D: A clotted sample gives clumps and fibrin strands, not a blood-like cell mix.
Question 5 · Hard
After chemotherapy for B-lymphoblastic leukemia, a 6-year-old's regenerating marrow has 12% CD19-positive, CD10-positive cells. They form a smooth spectrum from CD34-positive, CD20-negative cells to CD20-positive mature B cells, with no aberrant markers. The most likely interpretation is:
1. ARelapse of B-lymphoblastic leukemia
2. BMature B-cell lymphoma in the marrow
3. CMixed-phenotype acute leukemia
4. DNormal B-cell precursors (hematogones)
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Answer: D · Normal B-cell precursors (hematogones)
Hematogones are normal B-cell precursors that increase in regenerating marrow, especially in children after chemotherapy. On flow cytometry they show orderly maturation: CD34 and CD10 are lost and CD20 and CD45 are gained in a smooth continuum. Leukemic blasts instead form a tight cluster stuck at one stage, often with abnormal antigen levels or myeloid markers. Mistaking hematogones for relapse could lead to needless treatment.
- A: Relapsed blasts form a cluster stuck at one stage, not a smooth maturation spectrum.
- B: Mature lymphoma cells lack CD34 and show light-chain restriction.
- C: Mixed-phenotype leukemia needs blasts of two lineages, which is not seen here.
Question 6 · Medium
Some green FITC emission is detected in the channel meant for PE. The process that corrects for this spillover is:
1. AThreshold setting
2. BDoublet discrimination
3. CGating
4. DCompensation
Answer and explanation in LearnFree account
Question 7 · Easy
Compared with the aspirate smear, the trephine biopsy is better for assessing:
1. AThe differential cell percentages
2. BFine nuclear and cytoplasmic detail
3. CIron in developing red cells
4. DOverall marrow cellularity and architecture
Answer and explanation in LearnFree account
Question 8 · Easy
What makes cells pass through the laser of a flow cytometer one at a time?
1. ACentrifugal force in a spinning rotor
2. BMagnetic beads holding cells in line
3. CElectrical impedance across an aperture
4. DHydrodynamic focusing by sheath fluid
Answer and explanation in LearnFree account
Question 9 · Medium
A trephine biopsy from a 70-year-old shows 75% cellularity. Using the rule that normal cellularity is about 100 minus the age in years, this marrow is:
1. AHypocellular for age
2. BPacked (fully cellular)
3. CHypercellular for age
4. DNormocellular for age
Answer and explanation in LearnFree account
Question 10 · Easy
In adults, the preferred site for taking a bone marrow aspirate and trephine biopsy together is the:
1. ASternum
2. BPosterior iliac crest
3. CProximal tibia
4. DLumbar spine
Answer and explanation in LearnFree account
Question 11 · Easy
In flow cytometry, side-scattered light mainly reflects a cell's:
1. ASurface antigen density
2. BTotal DNA content
3. CInternal granularity
4. DOverall cell size
Answer and explanation in LearnFree account
Question 12 · Medium
Which stain is used to assess iron stores in a bone marrow aspirate?
1. ASudan black B
2. BPeriodic acid-Schiff (PAS)
3. CPerls' Prussian blue
4. DMyeloperoxidase
Answer and explanation in LearnFree account

Flow cytometry and bone marrow examination

Blood from a patient with lymphocytosis is stained for surface light chains, and the plot shows the CD19-positive B cells. What does it show?

Bone marrow from a patient with pancytopenia is analyzed by flow cytometry, plotting CD45 against side scatter. The population in gate R1, 62% of all events, is most likely made up of:

After chemotherapy for B-lymphoblastic leukemia, a 6-year-old's regenerating marrow has 12% CD19-positive, CD10-positive cells. They form a smooth spectrum from CD34-positive, CD20-negative cells to CD20-positive mature B cells, with no aberrant markers. The most likely interpretation is:

Some green FITC emission is detected in the channel meant for PE. The process that corrects for this spillover is:

Compared with the aspirate smear, the trephine biopsy is better for assessing:

What makes cells pass through the laser of a flow cytometer one at a time?

A trephine biopsy from a 70-year-old shows 75% cellularity. Using the rule that normal cellularity is about 100 minus the age in years, this marrow is:

In adults, the preferred site for taking a bone marrow aspirate and trephine biopsy together is the:

In flow cytometry, side-scattered light mainly reflects a cell's:

Which stain is used to assess iron stores in a bone marrow aspirate?