A 41-year-old man develops fever and a widespread rash 4 weeks after starting carbamazepine. The analyzer's differential is suppressed by an abnormal-scatter flag, so a direct eosinophil count is requested. Blood is diluted 1:20 in an eosin-based fluid that lyses the red cells and stains eosinophil granules. In an improved Neubauer chamber (depth 0.1 mm), all nine large squares (1 mm² each) are counted on both sides, giving 41 and 49 eosinophils. The reference value is below 0.5 × 10^9/L. What is the eosinophil count, and how is it interpreted?

0.10 × 10^9/L, within the reference range

0.05 × 10^9/L, within the reference range

Blood is diluted 1:100 in 1% ammonium oxalate, and platelets are counted in the outlined central square (1 mm², depth 0.1 mm), as shown. The platelet count is:

1,860 × 10^9/L (1,860,000/µL)

Blood is diluted 1:200 for a manual red cell count. The five counting squares of the central large square (depth 0.1 mm) contain 450 cells. The RBC count is:

4.50 × 10^12/L (4.50 × 10^6/µL)

22.5 × 10^12/L (22.5 × 10^6/µL)

0.45 × 10^12/L (0.45 × 10^6/µL)

0.90 × 10^12/L (0.90 × 10^6/µL)

Manual cell counts and hemocytometer

13 DOH Abu Dhabi (HAAD) lab licensing practice questions on Manual cell counts and hemocytometer, part of Hematology. The first 13 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 41-year-old man develops fever and a widespread rash 4 weeks after starting carbamazepine. The analyzer's differential is suppressed by an abnormal-scatter flag, so a direct eosinophil count is requested. Blood is diluted 1:20 in an eosin-based fluid that lyses the red cells and stains eosinophil granules. In an improved Neubauer chamber (depth 0.1 mm), all nine large squares (1 mm² each) are counted on both sides, giving 41 and 49 eosinophils. The reference value is below 0.5 × 10^9/L. What is the eosinophil count, and how is it interpreted?
1. A1.0 × 10^9/L, an eosinophilia
2. B0.10 × 10^9/L, within the reference range
3. C2.0 × 10^9/L, an eosinophilia
4. D0.05 × 10^9/L, within the reference range
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Answer: A · 1.0 × 10^9/L, an eosinophilia
The volume counted is 18 mm² × 0.1 mm = 1.8 µL, so the count is 90 × 20 ÷ 1.8 = 1,000 cells/µL, or 1.0 × 10^9/L. This is twice the upper reference value, an eosinophilia consistent with a drug hypersensitivity reaction. Dividing the cells from both sides by the volume of one side (0.9 µL) doubles the answer, leaving out the 0.1 mm depth gives a result ten times too low, and leaving out the dilution gives 0.05 × 10^9/L. A direct chamber count avoids multiplying a flagged, imprecise eosinophil percentage by the WBC.
- B: This leaves out the 0.1 mm chamber depth.
- C: This divides both sides' cells by one side's volume (0.9 µL).
- D: This leaves out the 1:20 dilution factor.
Question 2 · Medium
Blood is diluted 1:100 in 1% ammonium oxalate, and platelets are counted in the outlined central square (1 mm², depth 0.1 mm), as shown. The platelet count is:
Figure: MedExams
1. A18.6 × 10^9/L (18,600/µL)
2. B46.5 × 10^9/L (46,500/µL)
3. C1,860 × 10^9/L (1,860,000/µL)
4. D186 × 10^9/L (186,000/µL)
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Answer: D · 186 × 10^9/L (186,000/µL)
Count per µL = cells counted × dilution factor ÷ volume counted. The volume over the central square is 1 mm² × 0.1 mm = 0.1 µL. So 186 × 100 ÷ 0.1 = 186,000/µL, which is 186 × 10^9/L. In practice both sides are counted and must agree before the average is reported, and the result is checked against the film estimate.
- A: 18.6 × 10^9/L leaves out the 0.1 mm depth.
- B: 46.5 × 10^9/L divides by 4 as if four squares had been counted.
- C: 1,860 × 10^9/L divides by the depth twice.
Question 3 · Hard
Blood from a newborn with hemolytic disease is counted in an improved Neubauer chamber (depth 0.1 mm), with the counts shown. The film shows 25 nucleated red cells per 100 white cells. The corrected WBC count is:
Figure: MedExams
1. A9.4 × 10^9/L
2. B10.0 × 10^9/L
3. C12.5 × 10^9/L
4. D15.6 × 10^9/L
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Answer: B · 10.0 × 10^9/L
The four corner squares hold 58 + 63 + 61 + 68 = 250 cells in a volume of 4 × 0.1 = 0.4 µL. At a 1:20 dilution, 250 × 20 ÷ 0.4 = 12,500/µL, or 12.5 × 10^9/L. Acetic acid lyses mature red cells but not nucleated red cells, so these are included in the count. Corrected WBC = 12.5 × 100 ÷ (100 + 25) = 10.0 × 10^9/L.
- A: 9.4 × 10^9/L subtracts 25% instead of dividing by 125/100.
- C: 12.5 × 10^9/L is the uncorrected count, which still includes nucleated red cells.
- D: 15.6 × 10^9/L multiplies by 1.25 instead of dividing.
Question 4 · Easy
For a manual white cell count, cells are counted in the outlined squares of an improved Neubauer chamber, which is 0.1 mm deep. The total volume of diluted sample lying over these squares is:
Figure: MedExams
1. A0.4 µL
2. B0.9 µL
3. C4 µL
4. D0.04 µL
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Answer: A · 0.4 µL
The four outlined squares are the corner squares, each 1 mm × 1 mm. Their total area is 4 mm², and with a depth of 0.1 mm the volume is 4 × 0.1 = 0.4 mm³, which equals 0.4 µL. The count per microliter is then cells counted × dilution factor ÷ 0.4. Using the wrong volume is one of the commonest errors in manual counts.
- B: 0.9 µL is the volume over all nine large squares.
- C: 4 µL leaves out the 0.1 mm depth.
- D: 0.04 µL treats each corner square as 0.1 mm².
Question 5 · Hard
Blood is diluted 1:200 for a manual red cell count. The five counting squares of the central large square (depth 0.1 mm) contain 450 cells. The RBC count is:
1. A22.5 × 10^12/L (22.5 × 10^6/µL)
2. B4.50 × 10^12/L (4.50 × 10^6/µL)
3. C0.45 × 10^12/L (0.45 × 10^6/µL)
4. D0.90 × 10^12/L (0.90 × 10^6/µL)
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Answer: B · 4.50 × 10^12/L (4.50 × 10^6/µL)
Cells/µL = cells counted × dilution ÷ (area × depth). The five squares measure 5 × 0.04 = 0.2 mm², so 450 × 200 ÷ (0.2 × 0.1) = 4,500,000/µL, or 4.50 × 10^12/L. Errors in the area give 0.90 (using 1 mm²) or 22.5 (using one 0.04 mm² square), and leaving out the depth gives 0.45. Manual red cell counts are imprecise and now rarely used, but the same formula applies to every chamber count.
- A: 22.5 uses the area of only one small square.
- C: 0.45 leaves out the 0.1 mm depth.
- D: 0.90 uses the whole 1 mm² central square as the area.
Question 6 · Medium
In a manual WBC count at a 1:20 dilution, only 18 cells are seen in the four corner squares. Which change most improves the precision of the count?
1. ACount all nine large squares on both sides
2. BUse a 1:100 dilution and recount
3. CCount one side and double the result
4. DCount only the central large square
Answer and explanation in LearnFree account
Question 7 · Hard
A cloudy peritoneal fluid is diluted 1:10 in saline. Then 0.1 mL of this is mixed with 0.9 mL of acetic acid diluent. The four corner large squares on one side contain 100 white cells. What is the WBC count?
1. A25 × 10^9/L (25,000/µL)
2. B5.0 × 10^9/L (5,000/µL)
3. C2.5 × 10^9/L (2,500/µL)
4. D0.25 × 10^9/L (250/µL)
Answer and explanation in LearnFree account
Question 8 · Medium
The two sides of a hemocytometer give 96 and 151 white cells in the same squares. The laboratory requires the two sides to agree within 10%. The next step is to:
1. ARecount the same chamber filling
2. BReport the side with the higher count
3. CClean, remix and refill the chamber
4. DReport the mean of the two sides
Answer and explanation in LearnFree account
Question 9 · Medium
After a hemocytometer is filled for a manual platelet count, it is kept in a covered, moist Petri dish for about 10 minutes before counting. The purpose of this step is to:
1. ALet the diluent lyse the white cells
2. BLet the platelets take up the stain
3. CLet the platelets settle into one focal plane
4. DLet the platelets form countable clumps
Answer and explanation in LearnFree account
Question 10 · Easy
For a manual red cell count in an improved Neubauer chamber, cells are counted in five of the 25 squares in the central large square. What total area is counted?
1. A4 mm²
2. B0.2 mm²
3. C0.04 mm²
4. D1 mm²
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Question 11 · Medium
A bloody synovial fluid needs a manual white cell count. The usual 3% acetic acid diluent is avoided because acetic acid:
1. AMakes the red cells clump together
2. BFails to lyse the red cells in joint fluid
3. CForms a mucin clot with the hyaluronate
4. DLyses the white cells along with red cells
Answer and explanation in LearnFree account
Question 12 · Hard
A knee aspirate is diluted 1:20 in hypotonic saline for a manual count. A total of 270 white cells are counted in all nine large squares on one side of an improved Neubauer chamber (depth 0.1 mm). What is the WBC count?
1. A0.3 × 10^9/L (300/µL)
2. B0.6 × 10^9/L (600/µL)
3. C6.0 × 10^9/L (6,000/µL)
4. D54 × 10^9/L (54,000/µL)
Answer and explanation in LearnFree account
Question 13 · Hard
A CSF sample from a traumatic tap has red cells 10,000 × 10^6/L (10,000/µL) and white cells 50 × 10^6/L (50/µL). The patient's blood at the same time has WBC 8.0 × 10^9/L and RBC 4.0 × 10^12/L. What is the CSF white cell count corrected for the added blood?
1. A50 × 10^6/L (50/µL)
2. B20 × 10^6/L (20/µL)
3. C70 × 10^6/L (70/µL)
4. D30 × 10^6/L (30/µL)
Answer and explanation in LearnFree account

Manual cell counts and hemocytometer

Blood is diluted 1:100 in 1% ammonium oxalate, and platelets are counted in the outlined central square (1 mm², depth 0.1 mm), as shown. The platelet count is:

Blood from a newborn with hemolytic disease is counted in an improved Neubauer chamber (depth 0.1 mm), with the counts shown. The film shows 25 nucleated red cells per 100 white cells. The corrected WBC count is:

For a manual white cell count, cells are counted in the outlined squares of an improved Neubauer chamber, which is 0.1 mm deep. The total volume of diluted sample lying over these squares is:

Blood is diluted 1:200 for a manual red cell count. The five counting squares of the central large square (depth 0.1 mm) contain 450 cells. The RBC count is:

In a manual WBC count at a 1:20 dilution, only 18 cells are seen in the four corner squares. Which change most improves the precision of the count?

A cloudy peritoneal fluid is diluted 1:10 in saline. Then 0.1 mL of this is mixed with 0.9 mL of acetic acid diluent. The four corner large squares on one side contain 100 white cells. What is the WBC count?

The two sides of a hemocytometer give 96 and 151 white cells in the same squares. The laboratory requires the two sides to agree within 10%. The next step is to:

After a hemocytometer is filled for a manual platelet count, it is kept in a covered, moist Petri dish for about 10 minutes before counting. The purpose of this step is to:

For a manual red cell count in an improved Neubauer chamber, cells are counted in five of the 25 squares in the central large square. What total area is counted?

A bloody synovial fluid needs a manual white cell count. The usual 3% acetic acid diluent is avoided because acetic acid:

A knee aspirate is diluted 1:20 in hypotonic saline for a manual count. A total of 270 white cells are counted in all nine large squares on one side of an improved Neubauer chamber (depth 0.1 mm). What is the WBC count?

A CSF sample from a traumatic tap has red cells 10,000 × 10^6/L (10,000/µL) and white cells 50 × 10^6/L (50/µL). The patient's blood at the same time has WBC 8.0 × 10^9/L and RBC 4.0 × 10^12/L. What is the CSF white cell count corrected for the added blood?