MLT GlobeHematology: Platelets – page 2
90 Hematology MCQs on Platelets with answers and explanations.
A platelet count of 650 × 10^9/L in an adult is described as:
The adult platelet reference interval is roughly 150–400 × 10^9/L, so 650 × 10^9/L is thrombocytosis.
Thromboxane A2 released by activated platelets mainly causes:
Thromboxane A2, made through the cyclooxygenase pathway, recruits and aggregates more platelets and constricts vessels. Aspirin blocks its production.
During platelet aggregation, fibrinogen forms bridges between platelets by binding to which receptor?
Activated GP IIb/IIIa (integrin αIIbβ3) binds fibrinogen, linking platelets together. GP Ib/IX/V binds von Willebrand factor for adhesion, and P2Y12 is an ADP receptor.
In immune thrombocytopenia (ITP), the platelet count is low mainly because:
In ITP, autoantibodies coat platelets, which are then removed by splenic macrophages. Marrow megakaryocytes are normal or increased.
Pinpoint red spots in the skin caused by capillary bleeding in severe thrombocytopenia are called:
Petechiae are tiny (1–2 mm) pinpoint hemorrhages typical of platelet problems. Ecchymoses are larger bruises, and hemarthroses are joint bleeds seen in factor deficiencies.
The routine automated platelet count is performed on blood collected into which anticoagulant?
EDTA (lavender top) is the anticoagulant for CBC and platelet counts. Heparin can cause platelet clumping, and a clotted sample uses up platelets.
Primary hemostasis ends with the formation of:
Primary hemostasis is vessel constriction plus platelet adhesion and aggregation, forming a platelet plug. Secondary hemostasis (coagulation) then adds a stable fibrin mesh.
Which viral infection, common in South Asia, typically causes a marked fall in the platelet count?
Dengue commonly causes marked thrombocytopenia, and serial platelet counts are used to monitor patients.
A patient with aspirin intolerance needs antiplatelet therapy. Which drug, an ADP (P2Y12) receptor blocker, is a common alternative?
Clopidogrel blocks platelet P2Y12 receptors, a mechanism unrelated to cyclooxygenase. Ibuprofen is an NSAID that may cross-react; warfarin and heparin are anticoagulants.
A patient has a persistent platelet count of 900 × 10^9/L with a JAK2 mutation and no reactive cause. Most likely diagnosis?
Essential thrombocythemia is a myeloproliferative neoplasm with sustained thrombocytosis, often with JAK2, CALR or MPL mutations. The others lower platelet counts.
Which condition may lower the platelet count?
EBV infection can cause immune or splenic thrombocytopenia. Aspirin affects platelet function, not number; splenectomy and essential thrombocythemia raise counts.
Which statement correctly describes a megakaryocyte?
Megakaryocytes undergo endomitosis, replicating DNA without cell division, producing a single lobulated polyploid nucleus (up to 64N). They make platelets, not macrophages, and live mainly in marrow.
A child develops isolated platelets of 15 × 10^9/L two weeks after a viral illness; the rest of the CBC is normal. Which clinical finding is most typical?
Immune thrombocytopenia causes mucocutaneous bleeding. The spleen is not palpable; splenomegaly or sternal tenderness suggests another disorder, and hemarthrosis points to coagulation factor deficiency.
In which condition are prophylactic platelet transfusions generally avoided because transfused platelets are rapidly destroyed?
In ITP, autoantibodies clear donor platelets as quickly as the patient's own, so transfusion is reserved for life-threatening bleeding. Production failure states respond well to platelets.
Fever, confusion, platelets 12 × 10^9/L, schistocytes, normal PT/APTT and ADAMTS13 activity below 10%. The diagnosis is:
Severe ADAMTS13 deficiency defines TTP. DIC prolongs clotting times and lowers fibrinogen, ITP lacks schistocytes, and STEC-HUS has normal ADAMTS13 with prominent renal failure.
Roughly what fraction of the body's platelets is normally pooled in the spleen?
About a third of platelets are held in the spleen. In hypersplenism this pool enlarges, lowering the blood count; after splenectomy the count rises.
Which condition often causes purpura WITH a low platelet count?
SLE can cause immune thrombocytopenia. Vasculitis and HHT are vascular causes, and uremia impairs platelet function, all with a normal count.
An automated platelet count is 58 × 10^9/L (350 × 10^9/L yesterday), and the EDTA film shows platelet clumps. Best next step?
EDTA-dependent antibodies can clump platelets (pseudothrombocytopenia). Citrate usually prevents clumping; multiply the count by 1.1 for the citrate dilution.
Which result pattern is expected in isolated severe thrombocytopenia?
Low platelets impair primary hemostasis only, so bleeding time lengthens while clotting-factor tests stay normal. Abnormal PT/APTT with low fibrinogen suggests DIC.
An analyser reports platelets of 40 × 10^9/L in a well patient with no bleeding. The smear shows platelet clumps. The best action is:
EDTA can expose platelet antigens that antibodies bind, causing clumps and a falsely low count (pseudothrombocytopenia). Citrate usually prevents it; multiply the count by 1.1 for the dilution.