A 38-year-old woman has confusion and petechiae. Results: Hb 7.9 g/dL [79 g/L], platelets 9 × 10^3/µL [9 × 10^9/L], schistocytes 8%, LD 1,650 U/L (reference 100-225 U/L), haptoglobin 60%). Plasma from the citrate tube used for her PT at admission, before any treatment, was separated and frozen. The best action is:

Test the stored pretreatment plasma

Test ADAMTS13 on the admission EDTA tube

Repeat ADAMTS13 after the next exchange

Report that TTP has been excluded

A 34-year-old woman has confusion and fever. Results: Hb 7.6 g/dL (76 g/L), platelets 12 × 10^3/µL (12 × 10^9/L), many schistocytes, LD markedly raised, haptoglobin < 10 mg/dL (< 0.1 g/L), DAT negative, PT and APTT normal, creatinine 1.3 mg/dL (115 µmol/L). Which result would best confirm the most likely diagnosis?

ADAMTS13 activity of less than 10%

What does a high immature platelet fraction (IPF) suggest in a patient with thrombocytopenia?

Increased peripheral platelet destruction

Marrow replacement by leukemic blasts

Marrow suppression by chemotherapy

Reduced platelet production by marrow

A healthy blood donor's EDTA sample gives a platelet count of 42 × 10^3/µL (42 × 10^9/L). The film shows platelets ringed around neutrophils. What is the most likely explanation for the count?

Falsely low from an in vitro artifact

Truly low from pooling in the spleen

Truly low from failed production

Truly low from immune destruction

Platelets: quantitative disorders (ITP, TTP, HIT, pseudothrombocytopenia)

13 ASCP MLS practice questions on Platelets: quantitative disorders (ITP, TTP, HIT, pseudothrombocytopenia), 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 38-year-old woman has confusion and petechiae. Results: Hb 7.9 g/dL [79 g/L], platelets 9 × 10^3/µL [9 × 10^9/L], schistocytes 8%, LD 1,650 U/L (reference 100-225 U/L), haptoglobin < 10 mg/dL [< 0.1 g/L], DAT negative, PT and APTT normal, and creatinine 1.1 mg/dL [97 µmol/L]. Plasma exchange was started at once. The ADAMTS13 test was requested later and run on a citrate sample drawn after the first exchange: activity 46% (reference > 60%). Plasma from the citrate tube used for her PT at admission, before any treatment, was separated and frozen. The best action is:
1. ATest ADAMTS13 on the admission EDTA tube
2. BRepeat ADAMTS13 after the next exchange
3. CReport that TTP has been excluded
4. DTest the stored pretreatment plasma
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Answer: D · Test the stored pretreatment plasma
Schistocytes, severe thrombocytopenia, a high LD, absent haptoglobin, a negative DAT, normal clotting times and near-normal kidney function strongly suggest immune TTP, which is confirmed by ADAMTS13 activity below 10%. Plasma exchange replaces the patient's plasma with donor plasma that contains normal ADAMTS13, so a sample taken after the first exchange can give a falsely reassuring result. ADAMTS13 should therefore be measured on plasma collected before any plasma therapy, and the stored pretreatment citrate plasma is the right specimen. EDTA is unsuitable because it chelates the metal ions the enzyme needs, and a sample after the next exchange would be even more diluted with donor plasma. A post-exchange result cannot exclude TTP.
- A: EDTA chelates the zinc and calcium the enzyme needs, so EDTA plasma is not suitable.
- B: A later sample would contain even more donor plasma.
- C: A result after plasma exchange reflects donor ADAMTS13 and cannot exclude TTP.
Question 2 · Hard
A 34-year-old woman has confusion and fever. Results: Hb 7.6 g/dL (76 g/L), platelets 12 × 10^3/µL (12 × 10^9/L), many schistocytes, LD markedly raised, haptoglobin < 10 mg/dL (< 0.1 g/L), DAT negative, PT and APTT normal, creatinine 1.3 mg/dL (115 µmol/L). Which result would best confirm the most likely diagnosis?
1. AADAMTS13 activity of less than 10%
2. BPositive PF4-heparin antibody
3. CLow fibrinogen, high D-dimer
4. DShiga toxin found in stool
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Answer: A · ADAMTS13 activity of less than 10%
Microangiopathic hemolysis (schistocytes, high LD, absent haptoglobin, negative DAT) with severe thrombocytopenia, neurologic signs, mild kidney involvement and normal clotting times points to TTP. Severe ADAMTS13 deficiency, below 10% activity, confirms it, and an inhibitor assay shows the autoantibody in immune TTP. Blood for ADAMTS13 should be drawn before plasma exchange, because the plasma restores the enzyme. Treatment should not wait for the result.
- B: PF4-heparin antibodies support HIT, which causes thrombosis without schistocytic hemolysis.
- C: Low fibrinogen and high D-dimer suggest DIC, which would also prolong the PT and APTT.
- D: Shiga toxin supports HUS, which usually follows bloody diarrhea and causes severe kidney failure.
Question 3 · Easy
In primary immune thrombocytopenia (ITP), the autoantibodies most often bind to:
1. AThe ADAMTS13 enzyme
2. BGlycoprotein IIb/IIIa
3. CPF4-heparin complexes
4. DHLA class I antigens
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Answer: B · Glycoprotein IIb/IIIa
In ITP, IgG autoantibodies most often bind glycoprotein IIb/IIIa, and less often GPIb/IX. Coated platelets are removed by splenic macrophages through Fc receptors, and the antibodies also reduce platelet production by megakaryocytes. The marrow shows normal or increased megakaryocytes. ITP is a diagnosis of exclusion, with an otherwise normal blood count and film.
- A: Antibodies to ADAMTS13 cause immune TTP.
- C: PF4-heparin complexes are the target in heparin-induced thrombocytopenia.
- D: HLA class I antibodies cause platelet transfusion refractoriness, not ITP.
Question 4 · Medium
What does a high immature platelet fraction (IPF) suggest in a patient with thrombocytopenia?
1. AMarrow replacement by leukemic blasts
2. BMarrow suppression by chemotherapy
3. CIncreased peripheral platelet destruction
4. DReduced platelet production by marrow
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Answer: C · Increased peripheral platelet destruction
The IPF measures young, RNA-rich platelets recently released from the marrow. When platelets are destroyed or consumed in the circulation, as in ITP or TTP, the marrow releases more young platelets and the IPF rises. When production fails, as in aplastic anemia, leukemia or after chemotherapy, the IPF stays low or normal. It works like the reticulocyte count for red cells.
- A: Leukemic infiltration reduces megakaryocytes, so few young platelets are released.
- B: Chemotherapy suppresses megakaryocytes and lowers the IPF; a rising IPF signals recovery.
- D: Failing production gives a low or normal IPF.
Question 5 · Medium
A healthy blood donor's EDTA sample gives a platelet count of 42 × 10^3/µL (42 × 10^9/L). The film shows platelets ringed around neutrophils. What is the most likely explanation for the count?
1. ATruly low from pooling in the spleen
2. BTruly low from failed production
3. CFalsely low from an in vitro artifact
4. DTruly low from immune destruction
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Answer: C · Falsely low from an in vitro artifact
Platelet satellitism is an in vitro artifact in which platelets stick around neutrophils in EDTA blood. EDTA-dependent antibodies bind platelet glycoprotein IIb/IIIa and neutrophil Fc receptors, so the analyzer does not count these platelets. Like EDTA-induced clumping, it causes pseudothrombocytopenia in a person with no bleeding. A count on a sodium citrate sample or a fingerstick film shows the true value.
- A: Splenic pooling lowers the count in the body and needs an enlarged spleen.
- B: Failed production gives a true low count, usually with other cytopenias.
- D: Immune destruction lowers platelets in the body and does not form rings around neutrophils.
Question 6 · Medium
What is the basic defect in acquired (immune) thrombotic thrombocytopenic purpura?
1. ATissue factor activates clotting
2. BAutoantibody inhibits ADAMTS13
3. CShiga toxin damages endothelium
4. DAntibodies bind PF4-heparin
Answer and explanation in LearnFree account
Question 7 · Hard
A 57-year-old man with alcohol-related cirrhosis has a spleen of 19 cm. Results: Hb 11.2 g/dL (112 g/L), WBC 3.1 × 10^3/µL (3.1 × 10^9/L), platelets 64 × 10^3/µL (64 × 10^9/L). The film shows no schistocytes or clumps, and the platelets look normal. Which mechanism best explains the low platelet count?
1. APlatelet consumption in microthrombi
2. BPooling of platelets in the spleen
3. CAutoantibodies destroying platelets
4. DEDTA-dependent platelet clumping
Answer and explanation in LearnFree account
Question 8 · Medium
Compared with other causes of a low platelet count, the main clinical danger in heparin-induced thrombocytopenia is:
1. AKidney failure with schistocytes
2. BSevere mucosal bleeding
3. CNew venous or arterial thrombosis
4. DA platelet count below 10 × 10^3/µL (10 × 10^9/L)
Answer and explanation in LearnFree account
Question 9 · Hard
A 66-year-old woman receives unfractionated heparin after hip surgery. Platelets: day 0, 310 × 10^3/µL (310 × 10^9/L); day 4, 285 × 10^3/µL (285 × 10^9/L); day 8, 120 × 10^3/µL (120 × 10^9/L), with a new swollen, painful calf. Besides sending HIT antibody testing, the most appropriate step is:
1. AStop all heparin and start argatroban
2. BGive platelets and continue heparin
3. CStart warfarin and continue heparin
4. DSwitch to low-molecular-weight heparin
Answer and explanation in LearnFree account
Question 10 · Hard
A 31-year-old woman at 35 weeks' gestation has blood pressure of 168/110 mm Hg and proteinuria. Results: platelets 68 × 10^3/µL (68 × 10^9/L), schistocytes on the film, AST and ALT more than five times the upper reference limit, raised LD, PT and APTT normal, fibrinogen 430 mg/dL (4.3 g/L). The most likely cause of the low platelet count is:
1. AImmune thrombocytopenia
2. BDisseminated intravascular coagulation
3. CGestational thrombocytopenia
4. DHELLP syndrome
Answer and explanation in LearnFree account
Question 11 · Easy
A patient with no heparin exposure in the past year starts unfractionated heparin. When does the platelet count typically begin to fall in heparin-induced thrombocytopenia (HIT)?
1. A1 to 2 days after starting
2. B5 to 10 days after starting
3. C4 to 6 weeks after starting
4. DWithin hours of the first dose
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Question 12 · Medium
A 4-year-old girl develops oliguria 5 days after bloody diarrhea. She has schistocytes, platelets of 38 × 10^3/µL (38 × 10^9/L) and creatinine of 3.1 mg/dL (274 µmol/L). PT and APTT are normal, and ADAMTS13 activity is 72%. The most likely diagnosis is:
1. AShiga toxin-associated HUS
2. BImmune TTP
3. CImmune thrombocytopenia
4. DDisseminated intravascular coagulation
Answer and explanation in LearnFree account
Question 13 · Hard
A 58-year-old outpatient with no bruising has a platelet count of 36 × 10^3/µL (36 × 10^9/L) on an EDTA sample; a year ago it was normal. The analyzer flags the platelet histogram. Which finding would best show that this is pseudothrombocytopenia rather than immune thrombocytopenia?
1. ALarge platelets on the blood film
2. BMore marrow megakaryocytes
3. CA high immature platelet fraction
4. DA normal count on a citrate sample
Answer and explanation in LearnFree account

Platelets: quantitative disorders (ITP, TTP, HIT, pseudothrombocytopenia)

In primary immune thrombocytopenia (ITP), the autoantibodies most often bind to:

What does a high immature platelet fraction (IPF) suggest in a patient with thrombocytopenia?

A healthy blood donor's EDTA sample gives a platelet count of 42 × 10^3/µL (42 × 10^9/L). The film shows platelets ringed around neutrophils. What is the most likely explanation for the count?

What is the basic defect in acquired (immune) thrombotic thrombocytopenic purpura?

Compared with other causes of a low platelet count, the main clinical danger in heparin-induced thrombocytopenia is:

A patient with no heparin exposure in the past year starts unfractionated heparin. When does the platelet count typically begin to fall in heparin-induced thrombocytopenia (HIT)?

A 4-year-old girl develops oliguria 5 days after bloody diarrhea. She has schistocytes, platelets of 38 × 10^3/µL (38 × 10^9/L) and creatinine of 3.1 mg/dL (274 µmol/L). PT and APTT are normal, and ADAMTS13 activity is 72%. The most likely diagnosis is:

A 58-year-old outpatient with no bruising has a platelet count of 36 × 10^3/µL (36 × 10^9/L) on an EDTA sample; a year ago it was normal. The analyzer flags the platelet histogram. Which finding would best show that this is pseudothrombocytopenia rather than immune thrombocytopenia?