A 74-year-old man admitted with Mycoplasma pneumoniae pneumonia has a CBC on an EDTA sample that has stood at room temperature for 40 minutes. Impedance results: WBC 9.4 × 10^3/µL (9.4 × 10^9/L), RBC 1.86 × 10^6/µL (1.86 × 10^12/L), hemoglobin 10.9 g/dL (109 g/L), hematocrit 21.2% (0.212 L/L), MCV 114 fL, MCH 58.6 pg, MCHC 51.4 g/dL (514 g/L), platelets 205 × 10^3/µL (205 × 10^9/L). The plasma is clear and not hemolyzed. The blood film shows irregular clumps of red cells in the thin areas. What should be done first to obtain valid red cell results?

Warm the sample to 37 °C and rerun it

Recollect the sample in sodium citrate

Report the results with a spherocyte comment

Replace the plasma with diluent and rerun

A newborn's WBC is 18.6 × 10^3/µL (18.6 × 10^9/L) on an analyzer that includes nRBCs in the white cell count. The differential shows 55 nRBCs per 100 WBCs. What is the corrected WBC?

12.0 × 10^3/µL (12.0 × 10^9/L)

28.8 × 10^3/µL (28.8 × 10^9/L)

33.8 × 10^3/µL (33.8 × 10^9/L)

8.4 × 10^3/µL (8.4 × 10^9/L)

A sample has milky plasma and gives these results: RBC 4.40 × 10^6/µL (4.40 × 10^12/L), Hgb 17.2 g/dL (172 g/L), Hct 39.6% (0.396 L/L), MCV 90 fL, MCHC 43.4 g/dL (434 g/L). No red cell clumping is seen. What should be done to obtain a valid hemoglobin?

Replace plasma with diluent, then rerun

Recollect in citrate, then rerun

Warm the sample to 37 °C, then rerun

Dilute the sample 1:2, then rerun

Cell counts: spurious results

13 ASCP MLS practice questions on Cell counts: spurious results, 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 74-year-old man admitted with Mycoplasma pneumoniae pneumonia has a CBC on an EDTA sample that has stood at room temperature for 40 minutes. Impedance results: WBC 9.4 × 10^3/µL (9.4 × 10^9/L), RBC 1.86 × 10^6/µL (1.86 × 10^12/L), hemoglobin 10.9 g/dL (109 g/L), hematocrit 21.2% (0.212 L/L), MCV 114 fL, MCH 58.6 pg, MCHC 51.4 g/dL (514 g/L), platelets 205 × 10^3/µL (205 × 10^9/L). The plasma is clear and not hemolyzed. The blood film shows irregular clumps of red cells in the thin areas. What should be done first to obtain valid red cell results?
1. ARecollect the sample in sodium citrate
2. BReport the results with a spherocyte comment
3. CReplace the plasma with diluent and rerun
4. DWarm the sample to 37 °C and rerun it
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Answer: D · Warm the sample to 37 °C and rerun it
The pattern points to a cold agglutinin, typically anti-I after Mycoplasma infection. Clumps of red cells are counted as single large cells or fall outside the counting window, so the RBC count falls and the MCV rises; the calculated hematocrit (RBC × MCV) is then falsely low, and the MCH and MCHC become impossibly high. Hemoglobin is measured after lysis and stays correct, and the clear plasma rules out lipemia and hemolysis. Warming the sample to 37 °C for 15 to 30 minutes and rerunning it at once disperses the agglutinates. Plasma replacement with warm diluent is kept for agglutinates that persist after warming.
- A: Citrate is used for EDTA-dependent platelet clumping and does not stop cold red cell agglutination.
- B: Spherocytes raise the MCHC only slightly, and the film shows red cell clumps, not spherocytes.
- C: Plasma replacement is for lipemia, or for agglutinates that persist after warming; warming comes first.
Question 2 · Medium
An EDTA sample with a strong cold agglutinin is run at room temperature. Which result is still reliable?
1. AHemoglobin
2. BRBC count
3. CHematocrit
4. DMCHC
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Answer: A · Hemoglobin
Agglutinated red cells pass the aperture as clumps, so the RBC count falls and the MCV rises falsely. The hematocrit, calculated from the RBC count and MCV, is then falsely low, and the MCHC falsely high, often above 36 g/dL. Hemoglobin is measured after all the red cells are lysed, so clumping does not affect it. Warming the sample to 37 °C and rerunning usually corrects the other values.
- B: Clumps are counted as single cells or missed, so the RBC count is falsely low.
- C: The hematocrit is calculated from the falsely low RBC count.
- D: The MCHC is calculated from the falsely low hematocrit, so it is falsely high.
Question 3 · Hard
A patient with hepatitis C has these results at room temperature: WBC 14.8 × 10^3/µL (14.8 × 10^9/L), platelets 520 × 10^3/µL (520 × 10^9/L). After the sample is warmed to 37 °C: WBC 7.2 × 10^3/µL (7.2 × 10^9/L), platelets 240 × 10^3/µL (240 × 10^9/L). Red cell results do not change. The most likely cause is:
1. APlatelet clumping
2. BCryoglobulin
3. CCold agglutinin
4. DLipemia
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Answer: B · Cryoglobulin
Cryoglobulins precipitate in the cold, and the protein particles fall in the size ranges for platelets and white cells. Both counts rise falsely at room temperature and return to true values when the precipitate dissolves at 37 °C. Hepatitis C is a common cause of mixed cryoglobulinemia. Keeping the sample at 37 °C from collection to analysis prevents the error.
- A: Platelet clumping lowers the platelet count, while here it is falsely high.
- C: Cold agglutinins change red cell results, such as the RBC count and MCHC.
- D: Lipemia raises hemoglobin and is not corrected by warming.
Question 4 · Hard
A newborn's WBC is 18.6 × 10^3/µL (18.6 × 10^9/L) on an analyzer that includes nRBCs in the white cell count. The differential shows 55 nRBCs per 100 WBCs. What is the corrected WBC?
1. A28.8 × 10^3/µL (28.8 × 10^9/L)
2. B33.8 × 10^3/µL (33.8 × 10^9/L)
3. C12.0 × 10^3/µL (12.0 × 10^9/L)
4. D8.4 × 10^3/µL (8.4 × 10^9/L)
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Answer: C · 12.0 × 10^3/µL (12.0 × 10^9/L)
Corrected WBC = uncorrected WBC × 100 / (100 + nRBCs per 100 WBCs) = 18.6 × 100/155 = 12.0 × 10^3/µL (12.0 × 10^9/L). The 155 is used because the analyzer counted 155 nucleated cells for every 100 true white cells. Subtracting 55% instead gives 8.4, and multiplying by 155/100 gives 28.8. ASCP applies the correction when nRBCs exceed 10 per 100 WBCs (lab policies vary), which is common in newborns.
- A: 28.8 multiplies by 155/100, inverting the correction.
- B: 33.8 divides by 55 instead of by 155.
- D: 8.4 comes from subtracting 55% of the count instead of using 100/155.
Question 5 · Hard
A sample has milky plasma and gives these results: RBC 4.40 × 10^6/µL (4.40 × 10^12/L), Hgb 17.2 g/dL (172 g/L), Hct 39.6% (0.396 L/L), MCV 90 fL, MCHC 43.4 g/dL (434 g/L). No red cell clumping is seen. What should be done to obtain a valid hemoglobin?
1. ARecollect in citrate, then rerun
2. BWarm the sample to 37 °C, then rerun
3. CDilute the sample 1:2, then rerun
4. DReplace plasma with diluent, then rerun
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Answer: D · Replace plasma with diluent, then rerun
A high hemoglobin and MCHC with a normal RBC count, MCV and hematocrit means only the hemoglobin reading is wrong. With milky plasma and no clumping, the cause is turbidity from lipid. Centrifuging, replacing the plasma with an equal volume of diluent and rerunning gives a true hemoglobin, from which the MCH and MCHC are recalculated. Simple dilution does not help, because it leaves the ratio of lipid to hemoglobin unchanged.
- A: Citrate is used for EDTA-dependent platelet clumping, not for lipemia.
- B: Warming corrects cold agglutinins, which lower the RBC count; here the RBC count is normal.
- C: Diluting the whole sample dilutes lipid and hemoglobin equally, so the error remains.
Question 6 · Medium
A patient in diabetic ketoacidosis has a plasma glucose of 900 mg/dL (50.0 mmol/L). On an impedance analyzer, the CBC is most likely to show:
1. AFalsely low MCV and high MCHC
2. BFalsely low RBC count and high MCV
3. CFalsely high MCV and hematocrit, low MCHC
4. DFalsely high hemoglobin and MCHC
Answer and explanation in LearnFree account
Question 7 · Medium
On an analyzer without a dedicated nRBC channel, why do nucleated red cells falsely raise the WBC count?
1. AThey are larger than most mature white cells
2. BThey take up the stain used for granulocytes
3. CThey keep a nucleus after red cells are lysed
4. DThey resist lysis because of hemoglobin F
Answer and explanation in LearnFree account
Question 8 · Hard
An EDTA platelet count is 45 × 10^3/µL (45 × 10^9/L) and the film shows platelet clumps. A sodium citrate sample (9 parts blood to 1 part citrate) gives 120 × 10^3/µL (120 × 10^9/L). Which platelet count should be reported?
1. A45 × 10^3/µL (45 × 10^9/L)
2. B120 × 10^3/µL (120 × 10^9/L)
3. C108 × 10^3/µL (108 × 10^9/L)
4. D132 × 10^3/µL (132 × 10^9/L)
Answer and explanation in LearnFree account
Question 9 · Easy
Besides lowering the platelet count, EDTA-induced platelet clumps can falsely raise the:
1. AHematocrit
2. BHemoglobin value
3. CRed cell count
4. DWhite cell count
Answer and explanation in LearnFree account
Question 10 · Easy
Marked lipemia in a CBC sample falsely raises the:
1. AMCV
2. BRBC count
3. CHemoglobin
4. DHematocrit
Answer and explanation in LearnFree account
Question 11 · Hard
An inpatient's platelet count is 92 × 10^3/µL (92 × 10^9/L), down from 260 × 10^3/µL (260 × 10^9/L) yesterday. The draw was difficult. The film shows platelet clumps and fibrin strands, and the patient is not on heparin. The most likely cause is:
1. AHeparin-induced thrombocytopenia
2. BEDTA-dependent platelet clumping
3. CA partly clotted specimen
4. DPlatelet satellitism
Answer and explanation in LearnFree account
Question 12 · Medium
An automated platelet count is very low, but the blood film shows large platelet clumps and the patient has no bleeding. What should be done next?
1. AReport the count as critical thrombocytopenia
2. BRecount the same EDTA sample after refrigerating it
3. CRequest an urgent platelet transfusion
4. DRecollect in citrate and recount, correcting for dilution
Answer and explanation in LearnFree account
Question 13 · Medium
The WBC count is 15.0 × 10^9/L and the differential shows 25 nucleated red cells per 100 white cells. What is the corrected WBC count?
1. A12.0 × 10^9/L
2. B18.75 × 10^9/L
3. C15.0 × 10^9/L
4. D3.75 × 10^9/L
Answer and explanation in LearnFree account

Cell counts: spurious results

An EDTA sample with a strong cold agglutinin is run at room temperature. Which result is still reliable?

A newborn's WBC is 18.6 × 10^3/µL (18.6 × 10^9/L) on an analyzer that includes nRBCs in the white cell count. The differential shows 55 nRBCs per 100 WBCs. What is the corrected WBC?

A sample has milky plasma and gives these results: RBC 4.40 × 10^6/µL (4.40 × 10^12/L), Hgb 17.2 g/dL (172 g/L), Hct 39.6% (0.396 L/L), MCV 90 fL, MCHC 43.4 g/dL (434 g/L). No red cell clumping is seen. What should be done to obtain a valid hemoglobin?

A patient in diabetic ketoacidosis has a plasma glucose of 900 mg/dL (50.0 mmol/L). On an impedance analyzer, the CBC is most likely to show:

On an analyzer without a dedicated nRBC channel, why do nucleated red cells falsely raise the WBC count?

An EDTA platelet count is 45 × 10^3/µL (45 × 10^9/L) and the film shows platelet clumps. A sodium citrate sample (9 parts blood to 1 part citrate) gives 120 × 10^3/µL (120 × 10^9/L). Which platelet count should be reported?

Besides lowering the platelet count, EDTA-induced platelet clumps can falsely raise the:

Marked lipemia in a CBC sample falsely raises the:

An inpatient's platelet count is 92 × 10^3/µL (92 × 10^9/L), down from 260 × 10^3/µL (260 × 10^9/L) yesterday. The draw was difficult. The film shows platelet clumps and fibrin strands, and the patient is not on heparin. The most likely cause is:

An automated platelet count is very low, but the blood film shows large platelet clumps and the patient has no bleeding. What should be done next?

The WBC count is 15.0 × 10^9/L and the differential shows 25 nucleated red cells per 100 white cells. What is the corrected WBC count?