MLT GlobeHematology: Hemostasis & coagulation
125 Hematology MCQs on Hemostasis & coagulation with answers and explanations.
A boy has recurrent joint bleeds and his maternal uncle had the same problem. Which description best fits his disorder?
Hemophilia A and B are X-linked recessive, so affected males inherit the gene through carrier mothers. Deep joint and muscle bleeds, not mucosal bleeding, are typical.
Which anticoagulant prevents clotting mainly by enhancing antithrombin, thereby inactivating thrombin?
Heparin binds antithrombin and speeds its inhibition of thrombin and factor Xa. EDTA and citrate work by removing calcium; fluoride is a glycolysis inhibitor.
A patient with deep vein thrombosis suddenly becomes breathless with chest pain. Which complication is most likely?
A leg vein thrombus can break off and lodge in the pulmonary arteries. D-dimer and CT pulmonary angiography support the diagnosis.
Which laboratory test is used to monitor warfarin therapy?
Warfarin reduces vitamin K-dependent factors, and PT is most sensitive to factor VII; the INR standardizes PT across reagents. APTT is used for unfractionated heparin.
Which test is part of a routine coagulation screen?
A basic coagulation screen includes PT, APTT and often fibrinogen and thrombin time. ESR and WBC count assess inflammation; the indirect Coombs test is a blood bank test.
Hemophilia A results from deficiency of which coagulation factor?
Hemophilia A is factor VIII deficiency; hemophilia B (Christmas disease) is factor IX deficiency. Factor VII deficiency prolongs PT, not APTT.
Which coagulation factor does NOT need vitamin K for its synthesis in functional form?
Vitamin K is needed for gamma-carboxylation of factors II, VII, IX and X and proteins C and S. Factor XI is not vitamin K-dependent.
Which anticoagulant is used for routine PT and APTT testing?
Citrate binds calcium reversibly, and adding calcium in the assay restarts clotting. Blood-to-citrate ratio must be 9:1. Heparin inhibits clotting factors; EDTA is for CBCs.
A prolonged prothrombin time mainly reflects a problem in which part of coagulation?
PT tests factor VII (extrinsic) plus X, V, II and fibrinogen (common). APTT tests the intrinsic and common pathways.
How does EDTA prevent blood from clotting?
EDTA binds calcium irreversibly, and calcium is needed at several coagulation steps. This is why EDTA samples cannot be used for clotting tests.
A mesh of fibrin strands trapping red cells and platelets is known as what?
Thrombin turns fibrinogen into fibrin, which traps cells to form a clot. Plaque is an atheromatous lesion; rouleaux are stacked red cells.
In the common pathway, the prothrombinase complex (factor Xa, factor Va, Ca2+ and phospholipid) cleaves prothrombin to yield:
Prothrombinase converts prothrombin (factor II) to thrombin, which then cleaves fibrinogen to fibrin. Plasmin is generated from plasminogen during fibrinolysis.
A lavender-top (EDTA) tube arrives with several requests. Which test must be rejected and recollected?
Coagulation tests need citrated plasma; EDTA irreversibly binds calcium and affects factor V and VIII. EDTA samples are acceptable, even preferred, for grouping and antiglobulin testing.
Light-blue-top tubes for coagulation testing contain 3.2% sodium citrate, which prevents clotting by:
Citrate forms a soluble complex with calcium, reversibly; adding calcium back in the test restarts clotting. Heparin, not citrate, acts through antithrombin.
The APTT evaluates which parts of the coagulation cascade?
APTT is prolonged by deficiencies of XII, XI, IX, VIII and the common factors. The PT covers the extrinsic (factor VII) and common pathways.
Christmas disease (hemophilia B) results from deficiency of:
Hemophilia B is X-linked factor IX deficiency, clinically similar to hemophilia A. Factor-specific assays distinguish them.
Blood for coagulation tests is collected into citrate because the cascade's enzymatic complexes require:
Calcium bridges clotting factors to phospholipid surfaces. Citrate chelates calcium; recalcification restarts clotting in PT/APTT tests.
A boy with joint bleeds has a prolonged aPTT, normal PT and normal platelet count. The most likely deficiency is:
Hemarthrosis in a male with an isolated long aPTT points to hemophilia A (factor VIII), X-linked and the most common. Factor IX deficiency (hemophilia B) looks the same and is separated by factor assays.
A light-blue (3.2% sodium citrate) tube is only half filled. What is the effect on the PT and aPTT?
The correct ratio is 9 parts blood to 1 part citrate. With too little blood, excess citrate binds the calcium added in the test, so clotting times come out falsely long.
An aPTT reagent contains which components added to citrated plasma?
The aPTT uses phospholipid (partial thromboplastin) plus an activator such as silica, kaolin or ellagic acid, then calcium. Tissue factor is the PT reagent.