Components: platelets

6 ASCP MLS practice questions on Components: platelets, part of Blood Banking. 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 patient's 1-hour CCIs are repeatedly below 5,000 after ABO-identical platelets. There is no fever, bleeding or splenomegaly. The most likely cause is:

   1. AStorage damage to the platelets
   2. BAntibodies to HLA class II antigens
   3. CAntibodies to HLA class I antigens
   4. DAnti-D from earlier pregnancies

   Show answerHide answer

   Answer: C · Antibodies to HLA class I antigens

   A poor 1-hour increment on repeated transfusions, with no clinical cause, suggests immune refractoriness. Antibodies to HLA class I antigens, formed after pregnancy or transfusion, are the most common cause; platelet-specific (HPA) antibodies are less common. The patient is tested for HLA antibodies and given HLA-matched, antigen-negative or crossmatch-compatible platelets. Clinical causes such as fever and sepsis mainly shorten survival, so the 24-hour count falls more than the 1-hour count.

   • A: Storage damage would not explain repeatedly poor increments from many different units.
   • B: Platelets do not express HLA class II antigens.
   • D: Platelets do not carry the D antigen.

2. Question 2 · Medium

   An Rh-negative woman of childbearing age must receive Rh-positive platelets. What should be considered?

   1. AIrradiating the platelets
   2. BRh immune globulin, because platelet units contain a small amount of red cells
   3. CWashing the platelets
   4. DNothing, because Rh antibodies do not affect platelets

   Show answerHide answer

   Answer: B · Rh immune globulin, because platelet units contain a small amount of red cells

   Platelets do not carry the D antigen, but platelet units contain small amounts of red cells that can cause anti-D. Anti-D in a woman of childbearing potential can cause hemolytic disease in a future pregnancy. A standard dose of Rh immune globulin covers the red cells in many platelet units. In a thrombocytopenic patient the intravenous preparation avoids an intramuscular injection.

   • A: Irradiation prevents TA-GVHD and has no effect on anti-D formation.
   • C: Washing is not a routine way to prevent anti-D and damages platelets.
   • D: The risk comes from contaminating red cells, not from the platelets.

3. Question 3 · Easy

   In a 70 kg adult, one apheresis platelet unit is expected to raise the platelet count by about:

   1. A5 to 10 × 10^9/L
   2. B30 to 60 × 10^9/L
   3. C100 to 150 × 10^9/L
   4. D1 to 2 × 10^9/L

   Show answerHide answer

   Answer: B · 30 to 60 × 10^9/L

   One apheresis platelet unit should raise an adult's count by about 30 to 60 × 10^9/L (30,000 to 60,000/µL). One whole blood-derived unit raises it by about 5 to 10 × 10^9/L. Fever, sepsis, bleeding, splenomegaly and HLA antibodies reduce the increment. A count 10 to 60 minutes after transfusion shows whether the platelets survived.

   • A: 5 to 10 × 10^9/L is the rise from one whole blood-derived unit.
   • C: 100 to 150 × 10^9/L is far more than one unit gives.
   • D: 1 to 2 × 10^9/L would be a very poor response.

4. Question 4 · Hard

   A patient's platelet count is 8 × 10^9/L before and 32 × 10^9/L one hour after a transfusion of 4.0 × 10^11 platelets. Body surface area is 1.9 m². What is the corrected count increment (CCI), and what does it show?

   1. A11,400; an adequate response
   2. B6,000; platelet refractoriness
   3. C45,600; an adequate response
   4. D11,400; platelet refractoriness

   Show answerHide answer

   Answer: A · 11,400; an adequate response

   CCI = (post-count − pre-count, per µL) × BSA ÷ platelets given (× 10^11). Here (32,000 − 8,000) × 1.9 ÷ 4.0 = 11,400. A 1-hour CCI above about 7,500 is an adequate response. Values below 5,000 on two occasions suggest refractoriness.

   • B: 6,000 comes from leaving out the body surface area.
   • C: 45,600 comes from forgetting to divide by the platelet dose.
   • D: 11,400 is above the threshold, so it is not refractoriness.

5. Question 5 · Hard

   A 46-year-old man with acute myeloid leukemia has a temperature of 39.4 °C (102.9 °F), gram-negative bacteremia and an enlarged spleen. He receives one ABO-identical apheresis platelet unit containing 3.5 × 10^11 platelets. His body surface area is 1.75 m². Platelet counts: before transfusion 6 × 10^3/µL (6 × 10^9/L); 1 hour after 36 × 10^3/µL (36 × 10^9/L); 24 hours after 10 × 10^3/µL (10 × 10^9/L). The laboratory takes a 1-hour CCI above 7,500 and a 24-hour CCI above 4,500 as adequate. What do these results show?

   1. AAdequate response; continue routine platelet dosing
   2. BNonimmune consumption; HLA matching is not needed
   3. CHLA alloimmunization; HLA-matched platelets needed
   4. DToo small a dose; give two units next time

   Show answerHide answer

   Answer: B · Nonimmune consumption; HLA matching is not needed

   CCI = platelet increment (per µL) × body surface area (m²) ÷ platelets given (× 10^11). At 1 hour: 30,000 × 1.75 ÷ 3.5 = 15,000, a good immediate recovery. At 24 hours: 4,000 × 1.75 ÷ 3.5 = 2,000, a poor survival. A good 1-hour recovery followed by rapid loss points to nonimmune consumption, here from fever, sepsis and splenomegaly. HLA or HPA antibodies destroy platelets within minutes, so alloimmunization would give a low 1-hour CCI as well, and treating the underlying causes matters more than changing the platelet product.

   • A: The 24-hour CCI of 2,000 is below the adequate level of 4,500.
   • C: Alloimmunization lowers the 1-hour CCI, and here it is 15,000.
   • D: The dose was standard, and the 1-hour CCI shows it raised the count well.

6. Question 6 · Medium

   Why are platelets stored at 20 to 24 °C with continuous gentle agitation?

   1. ATo allow gas exchange that keeps pH acceptable
   2. BTo slow the growth of contaminating bacteria
   3. CTo keep the factor VIII in the plasma active
   4. DTo prevent hemolysis of contaminating red cells

   Answer and explanation in LearnFree account