A 77-year-old man with untreated chronic lymphocytic leukemia has a CBC on an impedance analyzer. Results: WBC 438 × 10^9/L (flagged above linearity), RBC 3.32 × 10^12/L, Hb 109 g/L (10.9 g/dL), Hct 0.35 L/L, MCV 105 fL, MCH 32.8 pg, MCHC 311 g/L. The plasma is clear after centrifugation. The film shows sheets of small mature lymphocytes and smudge cells, with normocytic red cells and no red cell agglutination. Last month, at a WBC of 95 × 10^9/L, his MCV was 91 fL. Which approach gives reliable red cell results?

Hb on a centrifuged lysate; RBC count minus the WBC

Dilute the sample 1:5; multiply the Hb and RBC by 5

Warm the sample to 37 °C; repeat the Hb and RBC count

Replace plasma with saline; repeat the Hb and RBC count

Late one morning, results from an impedance hematology analyzer start failing delta checks: several patients' RBC and platelet counts are 15-25% lower than the day before, while their WBC and Hb are unchanged. The technologist reruns the three QC levels: RBC and platelets are below −3 SD on every level, while WBC and Hb are within ±1 SD. The RBC and platelet histograms are broad and ragged, the RBC/platelet channel shows flow (count-time) warnings, and the background count on diluent alone is acceptable. The most likely cause, and the right action, is:

Partly blocked aperture: clean it, then rerun QC and patients

Contaminated diluent: replace it, then repeat the background

Deteriorated lysing reagent: replace it, then rerun the QC

RBC calibration drift: recalibrate, then rerun QC and patients

A 34-year-old woman taking carbimazole has fever and a sore throat; her WBC is 1.6 × 10^9/L. Her three-part WBC histogram is shown with a normal one. Which differential fits it?

Neutrophils 0.1, lymphocytes 1.3 × 10^9/L

Neutrophils 0.8, lymphocytes 0.7 × 10^9/L

Neutrophils 1.3, lymphocytes 0.1 × 10^9/L

Monocytes 1.2, lymphocytes 0.3 × 10^9/L

CBC, automated analyzers and histograms

22 DOH Abu Dhabi (HAAD) lab licensing practice questions on CBC, automated analyzers and histograms, part of Hematology. The first 22 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
A 77-year-old man with untreated chronic lymphocytic leukemia has a CBC on an impedance analyzer. Results: WBC 438 × 10^9/L (flagged above linearity), RBC 3.32 × 10^12/L, Hb 109 g/L (10.9 g/dL), Hct 0.35 L/L, MCV 105 fL, MCH 32.8 pg, MCHC 311 g/L. The plasma is clear after centrifugation. The film shows sheets of small mature lymphocytes and smudge cells, with normocytic red cells and no red cell agglutination. Last month, at a WBC of 95 × 10^9/L, his MCV was 91 fL. Which approach gives reliable red cell results?
1. ADilute the sample 1:5; multiply the Hb and RBC by 5
2. BWarm the sample to 37 °C; repeat the Hb and RBC count
3. CReplace plasma with saline; repeat the Hb and RBC count
4. DHb on a centrifuged lysate; RBC count minus the WBC
Show answerHide answer
Answer: D · Hb on a centrifuged lysate; RBC count minus the WBC
At a WBC of 438 × 10^9/L (0.44 × 10^12/L), the leukocytes cloud the hemoglobin reading and are counted with the red cells, so the Hb, RBC, Hct and MCV are all falsely raised. The Hb is read on a lysate that has been spun to remove the white cell debris, and the WBC is subtracted from the RBC count (3.32 − 0.44 = 2.88 × 10^12/L); the Hct is checked by spun microhematocrit, read below the buffy coat, and the indices are recalculated. Warming corrects cold agglutinins and saline replacement corrects lipemia, but the film shows no agglutination and the plasma is clear. Dilution lowers leukocytes and red cells in the same proportion, so the interference is unchanged, although a dilution is still needed to bring the WBC itself within linearity.
- A: Dilution keeps the leukocyte-to-red-cell ratio, so the error is unchanged.
- B: Warming corrects cold agglutinins; the film shows no agglutination.
- C: Saline replacement corrects lipemia; the plasma here is clear.
Question 2 · Hard
Late one morning, results from an impedance hematology analyzer start failing delta checks: several patients' RBC and platelet counts are 15-25% lower than the day before, while their WBC and Hb are unchanged. The technologist reruns the three QC levels: RBC and platelets are below −3 SD on every level, while WBC and Hb are within ±1 SD. The RBC and platelet histograms are broad and ragged, the RBC/platelet channel shows flow (count-time) warnings, and the background count on diluent alone is acceptable. The most likely cause, and the right action, is:
1. AContaminated diluent: replace it, then repeat the background
2. BDeteriorated lysing reagent: replace it, then rerun the QC
3. CRBC calibration drift: recalibrate, then rerun QC and patients
4. DPartly blocked aperture: clean it, then rerun QC and patients
Show answerHide answer
Answer: D · Partly blocked aperture: clean it, then rerun QC and patients
Only the RBC and platelet counts, which share one impedance aperture, are low on patients and controls alike; the WBC and the photometric Hb are unaffected. A partial blockage, usually protein or debris, slows the flow through the aperture so fewer cells are counted in the set time, and the ragged histograms and count-time warnings point to the same fault. The aperture is cleaned (by the cleaning cycle or manually), QC is rerun until acceptable, and patient samples run since the last good QC are retested. Recalibrating would build the blockage into the calibration, a lysing reagent fault affects the WBC rather than the red cells, and contaminated diluent raises the background and the counts.
- A: Contaminated diluent raises the background and the counts; the background is acceptable.
- B: The lysing reagent affects the WBC channel, which is in control.
- C: Drift does not cause ragged histograms or flow warnings; recalibrating would build in the fault.
Question 3 · Hard
A sample that reached the laboratory chilled gives RBC 2.48 × 10^12/L, Hb 118 g/L (11.8 g/dL), MCV 106 fL and MCHC 449 g/L (reference 320-360 g/L). Its RBC histogram is shown. Before the sample is warmed, which reported result is the most reliable?
Figure: MedExams
1. AHemoglobin concentration
2. BRed cell count
3. CMean cell volume
4. DHematocrit
Show answerHide answer
Answer: A · Hemoglobin concentration
The histogram has a main peak near 92 fL and a second peak at about twice that volume, with a small third one: pairs and triplets of agglutinated red cells counted as single large cells. Together with an impossible MCHC, this points to a cold agglutinin. Each clump is counted once, so the RBC count falls, the MCV rises and the calculated hematocrit (RBC × MCV) is wrong, which pushes the MCHC up. Hemoglobin is measured after all cells are lysed, so clumping does not affect it; warming the sample to 37 °C and rerunning corrects the other results.
- B: Each doublet or triplet is counted as one cell, so the count is falsely low.
- C: Clumps are sized as single large cells, so the MCV is falsely high.
- D: The hematocrit is calculated from the wrong RBC count and MCV.
Question 4 · Medium
A 34-year-old woman taking carbimazole has fever and a sore throat; her WBC is 1.6 × 10^9/L. Her three-part WBC histogram is shown with a normal one. Which differential fits it?
Figure: MedExams
1. ANeutrophils 0.8, lymphocytes 0.7 × 10^9/L
2. BNeutrophils 0.1, lymphocytes 1.3 × 10^9/L
3. CNeutrophils 1.3, lymphocytes 0.1 × 10^9/L
4. DMonocytes 1.2, lymphocytes 0.3 × 10^9/L
Show answerHide answer
Answer: B · Neutrophils 0.1, lymphocytes 1.3 × 10^9/L
In a three-part impedance differential, lysed lymphocytes form the small-volume peak, monocytes and other mid-sized cells the middle zone, and granulocytes the large-volume peak. The patient's histogram has a tall lymphocyte peak, a small mid zone and almost no granulocyte peak. With a WBC of 1.6 × 10^9/L this means severe neutropenia, which in a patient on carbimazole suggests drug-induced agranulocytosis. The count must be confirmed on a film and reported urgently.
- A: Nearly equal neutrophils and lymphocytes would leave a clear granulocyte peak.
- C: This would give a large granulocyte peak and almost no lymphocyte peak.
- D: Monocytosis would raise the mid zone, which is small here.
Question 5 · Medium
A 24-year-old woman has petechiae and a platelet count of 28 × 10^9/L, with normal Hb and WBC and no clumps on the film. Her platelet histogram is shown beside a normal one. The pattern best fits:
Figure: MedExams
1. AEDTA platelet clumping
2. BImmune thrombocytopenia (ITP)
3. CWiskott-Aldrich syndrome
4. DAplastic anemia
Show answerHide answer
Answer: B · Immune thrombocytopenia (ITP)
The patient's curve keeps its normal skewed shape but is shifted to the right, so the mean platelet volume is raised. In immune thrombocytopenia, platelets are destroyed early and the marrow responds by releasing young, large platelets. When the marrow itself fails, as in aplastic anemia, the platelets are normal-sized or small. A high MPV with a low count and a normal film is therefore a useful pointer to peripheral destruction.
- A: The film shows no clumps, and clumps do not shift the platelet curve to the right.
- C: Wiskott-Aldrich syndrome has small platelets, which would shift the curve to the left.
- D: Marrow failure gives normal or small platelets, not a right shift.
Question 6 · Hard
A CBC is run by mistake on a fully filled 3.2% sodium citrate tube (9 parts blood to 1 part citrate). Compared with an EDTA sample drawn at the same time, the results will show:
1. ACounts and hemoglobin about 10% low; indices little changed
2. BCounts unchanged; MCV and MCHC about 10% low
3. CAll results unchanged, as citrate only anticoagulates
4. DCounts and hemoglobin about 10% high; indices little changed
Answer and explanation in LearnFree account
Question 7 · Easy
At start-up, a hematology analyzer runs diluent alone through the counting system. This background check confirms that:
1. AControl material is within its stated limits
2. BPatient results match previous results
3. CCounts from reagents and debris are near zero
4. DThe calibration of the analyzer is still valid
Answer and explanation in LearnFree account
Question 8 · Medium
An EDTA sample is analyzed 36 hours after collection, having been kept at room temperature. The change most likely seen is:
1. AA rise in MCV as red cells swell
2. BA fall in hemoglobin as it breaks down
3. CA fall in MCV as red cells shrink
4. DA rise in MCHC as cells lose water
Answer and explanation in LearnFree account
Question 9 · Hard
A man with Bernard-Soulier syndrome has an impedance platelet count of 21 × 10^9/L, but the film shows about three times that number, many as large as red cells. Which method gives the most reliable count?
1. AImpedance count repeated after a 1:2 dilution
2. BImpedance count after warming the sample to 37 °C
3. CImpedance count repeated on a citrate sample
4. DFlow cytometric count with a CD61 antibody
Answer and explanation in LearnFree account
Question 10 · Medium
An RBC histogram is shifted to the left, and its base is much wider than normal. Which pattern does this show?
1. AMicrocytes of uniform size
2. BMicrocytes with marked anisocytosis
3. CMacrocytes with marked anisocytosis
4. DNormocytes with red cell agglutinates
Answer and explanation in LearnFree account
Question 11 · Medium
In a three-part impedance differential, the mid-sized fraction (often labelled MID or MXD) mainly contains:
1. ABlasts and immature granulocytes
2. BMonocytes, eosinophils and basophils
3. CLymphocytes and nucleated red cells
4. DSegmented neutrophils and bands
Answer and explanation in LearnFree account
Question 12 · Hard
A 24-year-old with Hb SC disease has an analyzer WBC of 17.6 × 10^9/L with a flag at the lower edge of the WBC histogram. The film estimate is about 8 × 10^9/L, with many target cells and no nucleated red cells, platelet clumps or giant platelets. The most likely cause of the discrepancy is:
1. ACold agglutinins clumping the red cells
2. BRed cells resistant to lysis, counted as white cells
3. CA true leukocytosis missed by the film estimate
4. DPlatelet satellitism around the neutrophils
Answer and explanation in LearnFree account
Question 13 · Hard
Over one afternoon, an analyzer's moving patient averages drift: MCV from 90 to 86 fL, MCH steady at 30 pg, and MCHC from 333 to 349 g/L. Which measurement has most likely drifted?
1. AHemoglobin photometry (Hb)
2. BRed cell counting (RBC)
3. CRed cell sizing (MCV/Hct)
4. DWhite cell lysis (WBC)
Answer and explanation in LearnFree account
Question 14 · Hard
A sample gives an MCHC of 375 g/L (37.5 g/dL) (reference 320-360 g/L). The plasma is clear and not hemolyzed, warming to 37 °C and rerunning gives the same result, and the film shows many spherocytes without clumps. What should the technologist do?
1. AIncubate at 37 °C for longer and rerun
2. BRequest a new sample for in vitro hemolysis
3. CReplace the plasma with diluent and rerun
4. DReport the result; spherocytes raise MCHC
Answer and explanation in LearnFree account
Question 15 · Easy
Why have most hematology analyzers replaced the cyanmethemoglobin reagent with sodium lauryl sulfate (SLS) for hemoglobin?
1. AIt needs no photometric reading
2. BIt also counts the red cells
3. CIt avoids toxic cyanide waste
4. DIt is the ICSH reference method
Answer and explanation in LearnFree account
Question 16 · Medium
What does Bull's moving average (XB analysis) track to monitor a hematology analyzer?
1. ARepeat counts on one retained patient sample
2. BRunning averages of patient MCV, MCH and MCHC
3. CMeans of the commercial control for each shift
4. DComparisons with manual hemocytometer counts
Answer and explanation in LearnFree account
Question 17 · Hard
A sample gives an MCHC of 392 g/L (39.2 g/dL) (reference 320-360 g/L), and the plasma is red after centrifugation. Which additional finding best shows that the hemolysis happened in the patient rather than in the tube?
1. AHemoglobinuria with a very low haptoglobin
2. BA raised potassium in the same sample
3. CA low RBC count and hematocrit
4. DRed plasma again on re-spinning the tube
Answer and explanation in LearnFree account
Question 18 · Medium
On an impedance WBC histogram, a tall rise at the far left edge, below the lymphocyte peak, is most often caused by:
1. AVery high numbers of neutrophils
2. BBlasts or immature granulocytes
3. CA raised eosinophil count
4. DPlatelet clumps or nucleated red cells
Answer and explanation in LearnFree account
Question 19 · Medium
On an impedance platelet histogram, the curve does not return to baseline at its upper end but rises again. What does this suggest?
1. ASmall red cells or giant platelets at the threshold
2. BA population of unusually small platelets
3. CDebris or electrical noise in the diluent
4. DPlatelet satellitism around neutrophils
Answer and explanation in LearnFree account
Question 20 · Easy
When two cells pass through an impedance aperture at the same time (coincidence), the analyzer tends to:
1. ACount one large cell instead of two
2. BReport a falsely high cell count
3. CReject the whole sample run
4. DCount each of the two cells twice
Answer and explanation in LearnFree account
Question 21 · Medium
On an impedance RBC histogram, what does the lower discriminator separate red cells from?
1. AWhite cells and large clumps
2. BRed cell doublets and agglutinates
3. CReticulocytes and nucleated red cells
4. DPlatelets and small debris
Answer and explanation in LearnFree account
Question 22 · Hard
A CBC shows a very high MCHC (above 37 g/dL), a high MCV and a low RBC count, and the film shows red cell clumping. What is the most likely cause, and what should be done?
1. ASevere iron deficiency anemia
2. BTrue hyperchromia caused by iron overload
3. CLipemia: replace the plasma with saline and rerun
4. DCold agglutinins: warm to 37 °C and rerun
Answer and explanation in LearnFree account

CBC, automated analyzers and histograms

A sample that reached the laboratory chilled gives RBC 2.48 × 10^12/L, Hb 118 g/L (11.8 g/dL), MCV 106 fL and MCHC 449 g/L (reference 320-360 g/L). Its RBC histogram is shown. Before the sample is warmed, which reported result is the most reliable?

A 34-year-old woman taking carbimazole has fever and a sore throat; her WBC is 1.6 × 10^9/L. Her three-part WBC histogram is shown with a normal one. Which differential fits it?

A 24-year-old woman has petechiae and a platelet count of 28 × 10^9/L, with normal Hb and WBC and no clumps on the film. Her platelet histogram is shown beside a normal one. The pattern best fits:

A CBC is run by mistake on a fully filled 3.2% sodium citrate tube (9 parts blood to 1 part citrate). Compared with an EDTA sample drawn at the same time, the results will show:

At start-up, a hematology analyzer runs diluent alone through the counting system. This background check confirms that:

An EDTA sample is analyzed 36 hours after collection, having been kept at room temperature. The change most likely seen is:

A man with Bernard-Soulier syndrome has an impedance platelet count of 21 × 10^9/L, but the film shows about three times that number, many as large as red cells. Which method gives the most reliable count?

An RBC histogram is shifted to the left, and its base is much wider than normal. Which pattern does this show?

In a three-part impedance differential, the mid-sized fraction (often labelled MID or MXD) mainly contains:

A 24-year-old with Hb SC disease has an analyzer WBC of 17.6 × 10^9/L with a flag at the lower edge of the WBC histogram. The film estimate is about 8 × 10^9/L, with many target cells and no nucleated red cells, platelet clumps or giant platelets. The most likely cause of the discrepancy is:

Over one afternoon, an analyzer's moving patient averages drift: MCV from 90 to 86 fL, MCH steady at 30 pg, and MCHC from 333 to 349 g/L. Which measurement has most likely drifted?

A sample gives an MCHC of 375 g/L (37.5 g/dL) (reference 320-360 g/L). The plasma is clear and not hemolyzed, warming to 37 °C and rerunning gives the same result, and the film shows many spherocytes without clumps. What should the technologist do?

Why have most hematology analyzers replaced the cyanmethemoglobin reagent with sodium lauryl sulfate (SLS) for hemoglobin?

What does Bull's moving average (XB analysis) track to monitor a hematology analyzer?

A sample gives an MCHC of 392 g/L (39.2 g/dL) (reference 320-360 g/L), and the plasma is red after centrifugation. Which additional finding best shows that the hemolysis happened in the patient rather than in the tube?

On an impedance WBC histogram, a tall rise at the far left edge, below the lymphocyte peak, is most often caused by:

On an impedance platelet histogram, the curve does not return to baseline at its upper end but rises again. What does this suggest?

When two cells pass through an impedance aperture at the same time (coincidence), the analyzer tends to:

On an impedance RBC histogram, what does the lower discriminator separate red cells from?

A CBC shows a very high MCHC (above 37 g/dL), a high MCV and a low RBC count, and the film shows red cell clumping. What is the most likely cause, and what should be done?