MLT GlobeHematology: Platelets
90 Hematology MCQs on Platelets with answers and explanations.
Which condition lowers the platelet count by reducing marrow production?
Aplastic anemia is marrow failure causing pancytopenia, including thrombocytopenia. Iron deficiency and splenectomy often raise platelets; polycythemia vera may raise them too.
Which cell is normally found only in bone marrow, not in circulating blood?
Megakaryocytes live in the marrow and release platelets into sinusoids; only occasional fragments reach the blood.
Platelets are released into the blood as cytoplasmic fragments of which bone marrow cell?
Megakaryocytes extend proplatelet processes into marrow sinusoids and shed platelets. Osteoclasts are also large marrow cells but resorb bone and derive from monocytes.
An isolated platelet count of 35 × 10^9/L most typically presents with:
Thrombocytopenia causes mucocutaneous bleeding such as epistaxis, gum bleeding and petechiae. Deep bleeding into joints and muscles is typical of coagulation factor deficiency.
Circulating platelets normally survive for about:
Platelets circulate for roughly 7–10 days before removal by the spleen and liver. 120 days is the red cell lifespan.
The usual adult reference interval for the platelet count is:
Most labs use about 150–400 × 10^9/L (150,000–400,000/µL). Below 150 is thrombocytopenia and above 450 is usually called thrombocytosis.
On a well-made smear, an average of 12 platelets is seen per oil-immersion field. Using a factor of 20, the estimated platelet count is:
Estimate = average per field × 20 × 10^9/L = 12 × 20 = 240 × 10^9/L. The estimate is used to check automated counts.
A well 5-year-old develops petechiae 2 weeks after a viral illness. Platelets are 12 × 10^9/L; Hb, WBC and smear are otherwise normal. The most likely diagnosis is:
Childhood ITP often follows a viral infection and shows isolated thrombocytopenia. Leukemia and aplastic anemia usually affect other cell lines.
A 4-year-old has bloody diarrhea, then acute kidney injury, schistocytes and thrombocytopenia. The most likely cause is:
Typical hemolytic uremic syndrome in children follows STEC (e.g. O157:H7) infection. ADAMTS13 is usually normal in HUS.
In light transmission aggregometry, platelet aggregation is detected as:
As platelets clump in stirred PRP, the plasma clears and more light passes through. Platelet-poor plasma serves as the 100% transmission reference.
Under high shear in arterioles, the first step of platelet adhesion to exposed collagen depends on:
Adhesion at high shear needs VWF to link collagen to platelet GPIb. GPIIb/IIIa–fibrinogen mediates the later aggregation step.
Bleeding from a platelet defect, rather than a coagulation factor deficiency, typically presents as:
Platelet and VWF disorders cause immediate mucocutaneous bleeding and petechiae. Hemarthroses and delayed bleeding suggest factor deficiencies such as hemophilia.
Megakaryocytes become large polyploid cells because they undergo:
Megakaryocytes replicate DNA without dividing (endomitosis), reaching 8N–64N ploidy, and then shed platelets from cytoplasmic extensions. They do not fuse or lose a nucleus to form platelets.
The normal life span of platelets in the circulation is about:
Platelets survive about 7–10 days and are then removed mainly by the spleen and liver. 120 days is the red cell life span.
Ten days after splenectomy for trauma, a previously healthy man's platelet count rises to 750 × 10^9/L. The best interpretation is:
Loss of the splenic pool and the stress of surgery commonly cause reactive thrombocytosis, which is often transient. ET needs persistent counts with a driver mutation or clonal marker.
A pregnant woman at 36 weeks has a platelet count of 115 × 10^9/L. She had normal counts before pregnancy and has no bleeding or hypertension. The most likely cause is:
Gestational thrombocytopenia is mild (usually above 70 × 10^9/L), appears late in pregnancy and resolves after delivery. HELLP includes hypertension, hemolysis and raised liver enzymes.
A patient with thrombocytopenia has a warm autoimmune hemolytic anemia with a positive DAT, and no other cause is found. This combination is called:
Evans syndrome is autoimmune destruction of two or more cell lines, usually AIHA with ITP. Kasabach-Merritt is platelet trapping in a vascular tumor.
In a bone marrow aspirate from a patient with immune thrombocytopenia, megakaryocytes are usually:
In ITP platelets are destroyed peripherally, so the marrow compensates with normal or increased megakaryocytes. Absent megakaryocytes suggest marrow failure such as aplastic anemia.
On a stained blood smear, normal platelets measure about:
Platelets are small cell fragments about 2–3 µm across, much smaller than a red cell (7–8 µm).
Which description fits a normal platelet on a Wright-stained smear?
Platelets have no nucleus. They are fragments of megakaryocyte cytoplasm with purple-staining granules.