Cell counts: reticulocytes

6 ASCP MLS practice questions on Cell counts: reticulocytes, part of Hematology. The first 6 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 66-year-old woman with pernicious anemia received her first intramuscular vitamin B12 injection 7 days ago. Today her hemoglobin is 7.3 g/dL (73 g/L), hematocrit 22% (0.22 L/L), MCV 112 fL and reticulocytes 18%, with marked polychromasia on the film. The laboratory uses a normal hematocrit of 45% and these maturation times for the reticulocyte production index: hematocrit 40-45%, 1.0 day; 35-39%, 1.5 days; 25-34%, 2.0 days; 15-24%, 2.5 days. What is her reticulocyte production index?

   1. A4.4
   2. B7.2
   3. C8.8
   4. D3.5

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   Answer: D · 3.5

   First correct the count for the low hematocrit: 18% × (22 ÷ 45) = 8.8%. Then divide by the maturation time for a hematocrit of 22%, which is 2.5 days: 8.8 ÷ 2.5 = 3.5. An index above 3 means the marrow is making red cells several times faster than normal, the expected response about a week after B12 replacement in megaloblastic anemia. Using the 2.0-day band gives 4.4, skipping the hematocrit correction gives 7.2, and stopping after the hematocrit correction gives 8.8. A rising reticulocyte count followed by a rising hemoglobin confirms that the treatment is working.

   • A: 4.4 uses a 2.0-day maturation time, which belongs to hematocrits of 25-34%.
   • B: 7.2 divides the raw 18% by 2.5 without first correcting for the low hematocrit.
   • C: 8.8 is the corrected count; the maturation time has not been applied.

2. Question 2 · Hard

   A 30-year-old woman with hemolytic anemia has a hematocrit of 25% (0.25 L/L) and reticulocytes of 12.6%. Using a normal hematocrit of 45% and a maturation time of 2.0 days, what is her reticulocyte production index?

   1. A6.3
   2. B7.0
   3. C3.5
   4. D11.3

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   Answer: C · 3.5

   First correct for the anemia: 12.6% × 25/45 = 7.0%. Then divide by the maturation time: 7.0 / 2.0 = 3.5. An RPI above 3 shows an adequate marrow response, as expected in hemolysis or after blood loss. An RPI below 2 points to poor red cell production, as in iron deficiency or marrow failure.

   • A: 6.3 skips the hematocrit correction.
   • B: 7.0 is the corrected count; it has not been divided by the maturation time.
   • D: 11.3 inverts the hematocrit ratio (45/25 instead of 25/45).

3. Question 3 · Medium

   A patient has an RBC count of 3.20 × 10^6/µL (3.20 × 10^12/L), a hematocrit of 27% (0.27 L/L) and reticulocytes of 4.0%. The absolute reticulocyte count is:

   1. A1,280 × 10^3/µL (1,280 × 10^9/L)
   2. B128 × 10^3/µL (128 × 10^9/L)
   3. C12.8 × 10^3/µL (12.8 × 10^9/L)
   4. D77 × 10^3/µL (77 × 10^9/L)

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   Answer: B · 128 × 10^3/µL (128 × 10^9/L)

   Absolute count = RBC count × reticulocyte fraction: 3.20 × 10^6/µL × 0.040 = 0.128 × 10^6/µL, or 128 × 10^3/µL (128 × 10^9/L). The ASCP reference range is 20 to 115 × 10^3/µL, so this count is raised. No hematocrit correction is applied, because the low RBC count already reflects the anemia. Using the hematocrit-corrected percentage (2.4%) gives 77, which counts the anemia twice.

   • A: This treats 4.0% as 0.40 instead of 0.040.
   • C: This is a decimal slip: 4.0% is 0.040, not 0.004.
   • D: This uses the hematocrit-corrected percentage, counting the anemia twice.

4. Question 4 · Medium

   When the hematocrit is low, the reticulocyte production index divides the corrected count by a maturation time of more than one day. Why?

   1. AFewer reticulocytes take up the stain in anemia
   2. BReticulocytes mature faster in the blood in anemia
   3. CAnemic blood dilutes the reticulocytes in the tube
   4. DShift reticulocytes stay longer in the blood

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   Answer: D · Shift reticulocytes stay longer in the blood

   Erythropoietin, raised in anemia, pushes reticulocytes out of the marrow early. These shift reticulocytes take longer than the usual 1 day to lose their RNA in the blood, so each is counted for longer and the count overstates daily production. The RPI corrects for this with about 1.5 days at a hematocrit of 35%, 2.0 days at 25% and 2.5 days at 15%. Shift reticulocytes appear as large polychromatic cells on the film.

   • A: Staining is not reduced in anemia; the correction is for time spent in the blood.
   • B: Early-released reticulocytes mature more slowly in the blood, not faster.
   • C: There is no dilution of reticulocytes in the tube.

5. Question 5 · Hard

   Reticulocyte count 6%, patient hematocrit 20%, normal hematocrit 45%. What is the corrected reticulocyte count?

   1. A2.7%
   2. B6%
   3. C13.5%
   4. D1.3%

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   Answer: A · 2.7%

   The corrected count adjusts for the smaller number of red cells in anemia: 6 × 20/45 = 2.7%. The reticulocyte production index goes further and divides by the maturation time in blood, about 2 days at a hematocrit of 20%, giving about 1.3. An index below 2 in anemia suggests an inadequate marrow response. These corrections stop anemia from making the marrow response look better than it is.

   • B: 6% is the uncorrected count.
   • C: 13.5% multiplies by 45/20 instead of 20/45.
   • D: 1.3 is the reticulocyte production index, not the corrected count.

6. Question 6 · Easy

   Which method is used to count reticulocytes?

   1. APrussian blue stain on a blood film
   2. BNew methylene blue stain or flow cytometry
   3. CSudan black B stain on a blood film
   4. DWright stain on a routine blood film

   Answer and explanation in LearnFree account