During an analyzer breakdown at a small clinic laboratory, a CBC on a 34-year-old woman is done by manual methods: cyanmethemoglobin Hb 128 g/L (12.8 g/dL), spun microhematocrit 0.33 L/L and hemocytometer RBC 4.20 × 10^12/L. Reference ranges: MCV 80-100 fL, MCH 27-33 pg, MCHC 320-360 g/L. The stained film shows normocytic, normochromic red cells with no spherocytes, target cells or agglutination, and the plasma in the hematocrit tube is clear. Before releasing the results, the technologist calculates the red cell indices. The best action is:

Repeat the microhematocrit before reporting

Repeat the hemoglobin on a fresh dilution

Repeat the hemocytometer red cell count

Report the indices with a spherocyte comment

Ten days after starting vitamin B12 injections for pernicious anemia, a man's MCV has fallen from 118 to 112 fL, while his RDW has risen from 17% to 23%. The best explanation is:

New normal-sized cells mixing with old macrocytes

Treatment failure from intrinsic factor antibodies

Analyzer drift in the volume measurement

Red cell fragments formed during the therapy

Red cell indices and calculations

14 DOH Abu Dhabi (HAAD) lab licensing practice questions on Red cell indices and calculations, part of Hematology. The first 14 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
During an analyzer breakdown at a small clinic laboratory, a CBC on a 34-year-old woman is done by manual methods: cyanmethemoglobin Hb 128 g/L (12.8 g/dL), spun microhematocrit 0.33 L/L and hemocytometer RBC 4.20 × 10^12/L. Reference ranges: MCV 80-100 fL, MCH 27-33 pg, MCHC 320-360 g/L. The stained film shows normocytic, normochromic red cells with no spherocytes, target cells or agglutination, and the plasma in the hematocrit tube is clear. Before releasing the results, the technologist calculates the red cell indices. The best action is:
1. ARepeat the hemoglobin on a fresh dilution
2. BRepeat the hemocytometer red cell count
3. CReport the indices with a spherocyte comment
4. DRepeat the microhematocrit before reporting
Show answerHide answer
Answer: D · Repeat the microhematocrit before reporting
The indices are MCV 0.33 ÷ 4.20 × 1,000 = 79 fL, MCH 128 ÷ 4.20 = 30.5 pg and MCHC 128 ÷ 0.33 = 388 g/L. The MCH, which uses only the Hb and the RBC count, is normal, while both indices that use the hematocrit (MCV and MCHC) disagree with the normocytic, normochromic film. A falsely low hematocrit explains both: a value of about 0.38 L/L would give an MCV near 90 fL and an MCHC near 337 g/L. The microhematocrit should be repeated and read at the top of the red cell column, below the buffy coat, before any result is released. An MCHC above 360 g/L with no spherocytes on the film signals a measurement error, not a red cell disorder.
- A: The normal MCH shows the Hb agrees with the RBC count; the error is in the hematocrit.
- B: The MCHC does not use the RBC count, and the normal MCH shows the count agrees with the Hb.
- C: There are no spherocytes, so an MCHC of 388 g/L means a measurement error.
Question 2 · Medium
Hemoglobin is 84 g/L (8.4 g/dL) and the RBC count is 4.20 × 10^12/L. What is the MCH?
1. A50 pg
2. B20 pg
3. C2.0 pg
4. D200 pg
Show answerHide answer
Answer: B · 20 pg
MCH (pg) = hemoglobin (g/L) ÷ RBC (× 10^12/L), so 84 ÷ 4.20 = 20 pg. Using hemoglobin in g/dL without the factor of 10 gives 2.0 pg, and inverting the ratio gives about 50 pg. An MCH of 20 pg is well below the usual reference of about 27-33 pg, which means hypochromia. Low MCH values are typical of iron deficiency and thalassemia.
- A: 50 pg comes from dividing the RBC count by the hemoglobin.
- C: 2.0 pg comes from using g/dL without the factor of 10.
- D: 200 pg comes from an extra factor of 10.
Question 3 · Hard
Ten days after starting vitamin B12 injections for pernicious anemia, a man's MCV has fallen from 118 to 112 fL, while his RDW has risen from 17% to 23%. The best explanation is:
1. ATreatment failure from intrinsic factor antibodies
2. BNew normal-sized cells mixing with old macrocytes
3. CAnalyzer drift in the volume measurement
4. DRed cell fragments formed during the therapy
Show answerHide answer
Answer: B · New normal-sized cells mixing with old macrocytes
Within days of B12 treatment the marrow releases a wave of new normocytic red cells, while the older macrocytes survive for weeks. The blood therefore holds two populations, so the spread of sizes (RDW) rises even as the average MCV starts to fall. The reticulocyte count peaks about a week after the first dose, and the MCV usually returns to normal over about two months. A rising RDW at this stage is an expected response, not a warning sign.
- A: Intrinsic factor antibodies block oral B12 absorption, not injected B12, and the falling MCV shows a response.
- C: Drift would shift every patient's MCV, not widen one patient's size range.
- D: Fragments would lower the MCV sharply and show on the film.
Question 4 · Medium
Two samples both have a red cell volume SD of 13.5 fL. Sample A has an MCV of 90 fL and sample B an MCV of 120 fL. What are their RDW-CV values?
1. AA 11.3%, B 15.0%
2. BA 6.7%, B 8.9%
3. CA 13.5%, B 13.5%
4. DA 15.0%, B 11.3%
Show answerHide answer
Answer: D · A 15.0%, B 11.3%
RDW-CV = SD ÷ MCV × 100, so A is 13.5 ÷ 90 × 100 = 15.0% and B is 13.5 ÷ 120 × 100 = 11.3%. The same spread of sizes gives a lower CV when the cells are larger, so RDW-CV can look normal in a macrocytic sample with real anisocytosis. RDW-SD, a direct width in fL, is not divided by the MCV and avoids this effect. Swapping the samples, quoting the SD itself, or dividing MCV by SD gives the other options.
- A: These values swap the two samples.
- B: These come from dividing MCV by SD instead of SD by MCV.
- C: 13.5 is the SD in fL, not the CV.
Question 5 · Hard
An analyzer that measures hematocrit directly reports Hct 0.30 L/L and MCV 75 fL, having calculated MCV from Hct ÷ RBC. What RBC count did it measure?
1. A2.25 × 10^12/L
2. B0.40 × 10^12/L
3. C4.00 × 10^12/L
4. D2.50 × 10^12/L
Show answerHide answer
Answer: C · 4.00 × 10^12/L
Rearranging MCV = Hct ÷ RBC × 1000 gives RBC = Hct ÷ MCV × 1000. Here 0.30 ÷ 75 = 0.004, and × 1000 = 4.00 × 10^12/L. The 2.50 option comes from dividing MCV by the hematocrit written as 30, and 2.25 from multiplying instead of dividing. Rearranging the index formulas lets the technologist check whether a printed set of results is internally consistent.
- A: 2.25 comes from multiplying the hematocrit by MCV.
- B: 0.40 comes from a misplaced decimal point.
- D: 2.50 comes from dividing MCV by the hematocrit written as 30.
Question 6 · Easy
A raised RDW tells the technologist that the red cells:
1. AAre larger on average than usual
2. BVary more than usual in shape
3. CVary more than usual in size
4. DHold less hemoglobin than usual
Answer and explanation in LearnFree account
Question 7 · Easy
Which two red cell indices are always calculated, never measured directly, on a hematology analyzer?
1. AHemoglobin and MCH
2. BMCH and MCHC
3. CRBC count and MCV
4. DMCV and hematocrit
Answer and explanation in LearnFree account
Question 8 · Hard
A report shows an MCV of 80 fL and an MCH of 26 pg, but the MCHC was not printed. The MCHC is:
1. A32.5 g/L (3.25 g/dL)
2. B308 g/L (30.8 g/dL)
3. C325 g/L (32.5 g/dL)
4. D260 g/L (26.0 g/dL)
Answer and explanation in LearnFree account
Question 9 · Hard
An impedance analyzer measures RBC 3.50 × 10^12/L, MCV 72 fL and hemoglobin 72 g/L (7.2 g/dL), and calculates the hematocrit first. What MCHC will it report?
1. A206 g/L (20.6 g/dL)
2. B100 g/L (10.0 g/dL)
3. C252 g/L (25.2 g/dL)
4. D286 g/L (28.6 g/dL)
Answer and explanation in LearnFree account
Question 10 · Medium
An impedance analyzer measures an RBC count of 5.60 × 10^12/L and an MCV of 64 fL. The hematocrit it reports is:
1. A0.36 L/L (36%)
2. B0.04 L/L (4%)
3. C0.11 L/L (11%)
4. D0.09 L/L (9%)
Answer and explanation in LearnFree account
Question 11 · Easy
MCHC is calculated by dividing the hemoglobin by the:
1. AMCH
2. BHematocrit
3. CRBC count
4. DMCV
Answer and explanation in LearnFree account
Question 12 · Medium
A hematocrit of 0.33 L/L and an RBC count of 3.00 × 10^12/L give an MCV of:
1. A91 fL
2. B99 fL
3. C110 fL
4. D11 fL
Answer and explanation in LearnFree account
Question 13 · Hard
A patient on intravenous lipid nutrition has very lipemic plasma, which falsely raises the analyzer's hemoglobin. The RBC count and MCV are measured correctly. Which indices will be falsely raised?
1. AMCV and MCH
2. BMCV and MCHC
3. CMCH and MCHC
4. DMCV, MCH and MCHC
Answer and explanation in LearnFree account
Question 14 · Medium
A woman with both iron and folate deficiency has an MCV of 88 fL (reference 80-100 fL). Which index best reveals the two red cell populations hidden by the normal MCV?
1. AA raised MCH
2. BA raised RDW
3. CA low hematocrit
4. DA raised MCHC
Answer and explanation in LearnFree account

Red cell indices and calculations

Hemoglobin is 84 g/L (8.4 g/dL) and the RBC count is 4.20 × 10^12/L. What is the MCH?

Ten days after starting vitamin B12 injections for pernicious anemia, a man's MCV has fallen from 118 to 112 fL, while his RDW has risen from 17% to 23%. The best explanation is:

Two samples both have a red cell volume SD of 13.5 fL. Sample A has an MCV of 90 fL and sample B an MCV of 120 fL. What are their RDW-CV values?

An analyzer that measures hematocrit directly reports Hct 0.30 L/L and MCV 75 fL, having calculated MCV from Hct ÷ RBC. What RBC count did it measure?

A raised RDW tells the technologist that the red cells:

Which two red cell indices are always calculated, never measured directly, on a hematology analyzer?

A report shows an MCV of 80 fL and an MCH of 26 pg, but the MCHC was not printed. The MCHC is:

An impedance analyzer measures RBC 3.50 × 10^12/L, MCV 72 fL and hemoglobin 72 g/L (7.2 g/dL), and calculates the hematocrit first. What MCHC will it report?

An impedance analyzer measures an RBC count of 5.60 × 10^12/L and an MCV of 64 fL. The hematocrit it reports is:

MCHC is calculated by dividing the hemoglobin by the:

A hematocrit of 0.33 L/L and an RBC count of 3.00 × 10^12/L give an MCV of:

A patient on intravenous lipid nutrition has very lipemic plasma, which falsely raises the analyzer's hemoglobin. The RBC count and MCV are measured correctly. Which indices will be falsely raised?

A woman with both iron and folate deficiency has an MCV of 88 fL (reference 80-100 fL). Which index best reveals the two red cell populations hidden by the normal MCV?