Why does the Wintrobe method give a slightly higher PCV than the microhematocrit method?

More plasma stays trapped between the packed red cells

Red cells swell in the wider Wintrobe tube

The buffy coat is read as part of the red cells

EDTA shrinks the red cells in the capillary tube

Hematology: PCV, ESR, indices and osmotic fragility

22 Kerala PSC Lab Technician Gr II practice questions on Hematology: PCV, ESR, indices and osmotic fragility, part of Pathology. 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 · Easy
What does the buffy coat above the packed red cells in a PCV tube contain?
1. ALysed red cells
2. BFibrinogen and plasma proteins
3. CReticulocytes
4. DWhite cells and platelets
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Answer: D · White cells and platelets
When anticoagulated blood is spun, red cells pack at the bottom, plasma stays on top, and a thin greyish-white layer forms between them. This buffy coat contains the white cells and platelets. It is left out when the PCV is read, and its thickness gives a rough idea of the WBC count. Smears made from the buffy coat concentrate abnormal cells and blood parasites.
- A: Lysed red cells release hemoglobin that colours the plasma red.
- B: Fibrinogen and other proteins stay dissolved in the plasma.
- C: Reticulocytes are less dense than older red cells and gather at the top of the red cell column, below the buffy coat.
Question 2 · Hard
A 30-year-old man's sample gives Hb 9.0 g/dL, PCV 30% and RBC 4.5 million/µL. Reference ranges: MCV 80-100 fL, MCH 27-32 pg, MCHC 32-36 g/dL. The red cells are:
1. AMicrocytic and normochromic
2. BMicrocytic and hypochromic
3. CNormocytic and normochromic
4. DMacrocytic and hypochromic
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Answer: B · Microcytic and hypochromic
MCV = PCV × 10 ÷ RBC (millions/µL) = 30 × 10 ÷ 4.5 = 67 fL, which is low. MCH = Hb × 10 ÷ RBC = 9.0 × 10 ÷ 4.5 = 20 pg, and MCHC = Hb × 100 ÷ PCV = 9.0 × 100 ÷ 30 = 30 g/dL; both are low. Small cells carrying less hemoglobin are microcytic and hypochromic, as in iron deficiency or thalassemia. The smear should be checked to confirm the indices.
- A: MCH 20 pg and MCHC 30 g/dL are both low, so the cells are hypochromic.
- C: The MCV of 67 fL is below 80 fL, so the cells are not normocytic.
- D: The MCV is low, not above 100 fL.
Question 3 · Easy
The Westergren ESR tube is graduated from 0 to:
1. A100 mm
2. B150 mm
3. C200 mm
4. D300 mm
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Answer: C · 200 mm
The Westergren tube is about 300 mm long with a bore of about 2.5 mm, and it is graduated from 0 to 200 mm. Citrated blood (4 volumes of blood to 1 volume of trisodium citrate) is filled to the zero mark and the tube is kept exactly vertical at room temperature. The height of the clear plasma column is read at exactly 1 hour. The shorter Wintrobe tube is graduated 0-100 mm and can also be used for the PCV.
- A: 0-100 mm is the scale of the Wintrobe tube.
- B: The Westergren scale runs to 200 mm, not 150 mm.
- D: About 300 mm is the total length of the tube, not its scale.
Question 4 · Medium
How do the red cells of a child with beta-thalassemia major behave in the osmotic fragility test?
1. ADecreased osmotic fragility
2. BLysis in isotonic saline
3. CIncreased osmotic fragility
4. DNormal osmotic fragility
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Answer: A · Decreased osmotic fragility
Thalassemic red cells are thin target cells with a large surface area for their small volume. They can take in more water before bursting, so they resist lysis until the saline is more dilute than normal cells can bear: osmotic fragility is decreased. Iron deficiency and liver disease with target cells behave the same way. Spherocytes, with little spare surface, show increased fragility.
- B: Even fragile cells do not lyse in isotonic (0.85%) saline.
- C: Increased fragility is the feature of spherocytes, as in hereditary spherocytosis.
- D: Target cells have a high surface-to-volume ratio, so their fragility is not normal.
Question 5 · Medium
Why does the Wintrobe method give a slightly higher PCV than the microhematocrit method?
1. ARed cells swell in the wider Wintrobe tube
2. BMore plasma stays trapped between the packed red cells
3. CThe buffy coat is read as part of the red cells
4. DEDTA shrinks the red cells in the capillary tube
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Answer: B · More plasma stays trapped between the packed red cells
The Wintrobe tube is spun at a much lower force (about 2,000-2,300 g for 30 minutes) than a microhematocrit capillary (10,000 g or more for 5 minutes). Packing is less complete, so more plasma stays trapped between the red cells and the reading is slightly higher. The microhematocrit is therefore preferred, and it needs only a fingerprick sample. In both methods the buffy coat is excluded from the reading.
- A: Red cells do not swell because of the width of the tube.
- C: The buffy coat is excluded in both methods when read correctly.
- D: The same EDTA sample can be used for both methods, so EDTA does not explain the difference.
Question 6 · Medium
Why does the Westergren method show a raised ESR more reliably than the Wintrobe method?
1. AIts longer column lets cells fall further
2. BIt uses EDTA blood without any dilution
3. CIt is read after 2 hours instead of 1
4. DIts tube is wider, so cells settle faster
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Question 7 · Easy
Which of the following does NOT raise the ESR?
1. ASevere anemia
2. BMultiple myeloma
3. CPolycythemia
4. DPregnancy
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Question 8 · Easy
In the microhematocrit method, capillary tubes are spun at about 10,000-12,000 g for:
1. A60 minutes
2. B5 minutes
3. C30 minutes
4. D1 minute
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Question 9 · Medium
Spherocytes lyse in saline concentrations that normal red cells tolerate because they have a:
1. AHigh content of fetal hemoglobin
2. BLow surface area to volume ratio
3. CWeak bond with oxygen
4. DDeficiency of G6PD enzyme
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Question 10 · Hard
Only 0.5 mL of blood was drawn into a 3 mL EDTA tube from a 40-year-old man. Plasma is clear, not hemolysed. Hb 13.2 g/dL, microhematocrit PCV 34%; last month Hb 13.4 g/dL, PCV 41%. Reference MCHC 32-36 g/dL. What best explains today's MCHC?
1. AHereditary spherocytosis
2. BLipemia raising the hemoglobin
3. CExcess EDTA shrinking the red cells
4. DCold agglutinins clumping the cells
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Question 11 · Hard
An EDTA sample for ESR was left on the bench at room temperature for 9 hours before the Westergren test was set up. The ESR is lower than the patient's raised CRP would suggest. Why?
1. AFibrinogen rises in stored blood at room temperature
2. BEDTA slowly lyses the red cells on standing
3. CWater evaporates from the sample on standing
4. DStored cells turn spherical and form fewer rouleaux
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Question 12 · Medium
A 58-year-old man has Hb 19.5 g/dL, PCV 60% and splenomegaly. What ESR is expected?
1. ANormal for age
2. BVery low
3. CVery high
4. DModerately raised
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Question 13 · Easy
The Wintrobe tube, used for both ESR and PCV, is graduated from:
1. A0 to 200 mm
2. B0 to 50 mm
3. C0 to 150 mm
4. D0 to 100 mm
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Question 14 · Medium
A correctly measured, non-lipemic sample has an MCHC of 38 g/dL. Which red cell abnormality should be looked for on the smear?
1. ATarget cells
2. BMacrocytes
3. CSpherocytes
4. DPencil cells
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Question 15 · Hard
A 7-year-old girl has jaundice, splenomegaly and many spherocytes; MCHC is 37 g/dL and osmotic fragility is increased. Her father had a splenectomy. Before reporting hereditary spherocytosis, which test must be negative?
1. ADirect antiglobulin test
2. BSickling test
3. CBone marrow iron stain
4. DHemoglobin electrophoresis
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Question 16 · Easy
Which red cell index is calculated as (hemoglobin in g/dL / PCV in %) x 100?
1. AMCV
2. BRDW
3. CMCH
4. DMCHC
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Question 17 · Hard
A 50-year-old man has Hb 9.0 g/dL, PCV 30% and RBC 2.5 million/µL. What is his MCV, and what type of anemia does it suggest?
1. A12 fL; microcytic
2. B83 fL; normocytic
3. C120 fL; macrocytic
4. D36 fL; microcytic
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Question 18 · Easy
In the osmotic fragility test, normal red cells are completely lysed at about which sodium chloride concentration?
1. A0.30%
2. B0.50%
3. C0.65%
4. D0.85%
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Question 19 · Medium
A Westergren ESR tube was left leaning against the wall of the rack instead of standing upright. How will this affect the result?
1. AIt will be falsely raised
2. BIt will be falsely lowered
3. CIt will not change
4. DIt will show hemolysis
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Question 20 · Easy
Which red cell index is used first to classify an anemia as microcytic, normocytic or macrocytic?
1. AESR
2. BMCHC
3. CMCV
4. DMCH
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Question 21 · Easy
Which plasma protein contributes most to rouleaux formation and a raised ESR?
1. ATransferrin
2. BFibrinogen
3. CAlbumin
4. DPrealbumin
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Question 22 · Medium
Why is heparinised or defibrinated blood, not oxalated or citrated blood, used for the osmotic fragility test?
1. AOxalate and citrate cause rouleaux
2. BOxalate and citrate lyse the red cells
3. CHeparin makes the red cells more fragile
4. DAdded salts would change the tonicity
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Hematology: PCV, ESR, indices and osmotic fragility

What does the buffy coat above the packed red cells in a PCV tube contain?

A 30-year-old man's sample gives Hb 9.0 g/dL, PCV 30% and RBC 4.5 million/µL. Reference ranges: MCV 80-100 fL, MCH 27-32 pg, MCHC 32-36 g/dL. The red cells are:

The Westergren ESR tube is graduated from 0 to:

How do the red cells of a child with beta-thalassemia major behave in the osmotic fragility test?

Why does the Wintrobe method give a slightly higher PCV than the microhematocrit method?

Why does the Westergren method show a raised ESR more reliably than the Wintrobe method?

Which of the following does NOT raise the ESR?

In the microhematocrit method, capillary tubes are spun at about 10,000-12,000 g for:

Spherocytes lyse in saline concentrations that normal red cells tolerate because they have a:

Only 0.5 mL of blood was drawn into a 3 mL EDTA tube from a 40-year-old man. Plasma is clear, not hemolysed. Hb 13.2 g/dL, microhematocrit PCV 34%; last month Hb 13.4 g/dL, PCV 41%. Reference MCHC 32-36 g/dL. What best explains today's MCHC?

An EDTA sample for ESR was left on the bench at room temperature for 9 hours before the Westergren test was set up. The ESR is lower than the patient's raised CRP would suggest. Why?

A 58-year-old man has Hb 19.5 g/dL, PCV 60% and splenomegaly. What ESR is expected?

The Wintrobe tube, used for both ESR and PCV, is graduated from:

A correctly measured, non-lipemic sample has an MCHC of 38 g/dL. Which red cell abnormality should be looked for on the smear?

A 7-year-old girl has jaundice, splenomegaly and many spherocytes; MCHC is 37 g/dL and osmotic fragility is increased. Her father had a splenectomy. Before reporting hereditary spherocytosis, which test must be negative?

Which red cell index is calculated as (hemoglobin in g/dL / PCV in %) x 100?

A 50-year-old man has Hb 9.0 g/dL, PCV 30% and RBC 2.5 million/µL. What is his MCV, and what type of anemia does it suggest?

In the osmotic fragility test, normal red cells are completely lysed at about which sodium chloride concentration?

A Westergren ESR tube was left leaning against the wall of the rack instead of standing upright. How will this affect the result?

Which red cell index is used first to classify an anemia as microcytic, normocytic or macrocytic?

Which plasma protein contributes most to rouleaux formation and a raised ESR?

Why is heparinised or defibrinated blood, not oxalated or citrated blood, used for the osmotic fragility test?