MLT GlobeHematology: Hemostasis & coagulation – page 2
125 Hematology MCQs on Hemostasis & coagulation with answers and explanations.
The usual adult reference interval for plasma fibrinogen is about:
Normal fibrinogen is roughly 2–4 g/L. It is an acute-phase reactant and rises in inflammation and pregnancy.
Von Willebrand factor has two main roles in hemostasis. They are:
VWF bridges platelet GPIb to exposed collagen and protects factor VIII from rapid clearance. Fibrinogen conversion is done by thrombin.
Factor V Leiden causes thrombophilia because the abnormal factor V:
The R506Q mutation removes an APC cleavage site, so factor Va stays active longer. It is the most common inherited thrombophilia in people of European ancestry.
Vitamin K is needed for which step in the synthesis of factors II, VII, IX and X?
Vitamin K is a cofactor for gamma-glutamyl carboxylase; the Gla residues let these factors bind calcium and phospholipid surfaces. Proteins C and S depend on the same step.
A light-blue citrate tube contains a small clot. The correct action is to:
Clotting consumes fibrinogen and factors and activates others, making results unreliable. Clotted coagulation samples must be rejected.
Unfractionated heparin acts as an anticoagulant mainly by:
A pentasaccharide sequence in heparin binds antithrombin, increasing its activity about 1000-fold. Longer chains are needed to bridge antithrombin to thrombin.
An elderly man with poor diet has perifollicular hemorrhages, corkscrew hairs and bleeding gums. PT, aPTT and platelets are normal. The likely cause is:
Scurvy weakens collagen in vessel walls, giving vascular bleeding with normal coagulation tests and platelet count. Vitamin K deficiency would prolong the PT.
Coagulation factor I is:
Factor I is fibrinogen, factor II prothrombin, factor III tissue factor and factor IV calcium.
Coagulation factor IV is:
Factor IV is calcium, which several clotting complexes need. Citrate and EDTA prevent clotting by removing it. Proaccelerin is factor V.
Which coagulation factor belongs only to the extrinsic pathway?
Factor VII, activated with tissue factor, is unique to the extrinsic pathway, which is measured by the PT. Factors VIII and IX are intrinsic, and X is in the common pathway.
Light-blue sodium citrate tubes for coagulation tests are designed to give a blood-to-anticoagulant ratio of:
Coagulation tubes are filled to give 9 parts blood to 1 part 3.2% citrate. The 4:1 ratio is used for the Westergren ESR.
Which enzyme breaks down fibrin in a clot?
Plasmin, formed from plasminogen by tissue plasminogen activator, digests fibrin. Thrombin forms fibrin, and factor XIIIa cross-links it.
Unfractionated heparin therapy is commonly monitored with which test?
The aPTT is the traditional test for monitoring unfractionated heparin (anti-Xa assays are also used). The PT/INR monitors warfarin.
Which drug is given to reverse an overdose of unfractionated heparin?
Protamine sulfate binds heparin and neutralizes it. Vitamin K reverses warfarin, and tranexamic acid inhibits fibrinolysis.
The specific antidote that restores the vitamin K–dependent factors in a patient on warfarin is:
Warfarin blocks vitamin K recycling. Giving vitamin K allows the liver to make functional factors II, VII, IX and X again.
The first response of a blood vessel to injury is:
Injured vessels constrict at once to reduce blood flow. Platelet plug formation and coagulation follow, and fibrinolysis comes last.
For the Ivy bleeding time, where is the incision made and what cuff pressure is kept?
The Ivy method uses a standardized incision on the volar forearm with the cuff at 40 mmHg. The older Duke method uses the earlobe. Veins are never used.
Mucosal bleeding and petechiae are typical of primary hemostasis defects. Which disorder usually does NOT present this way?
Hemophilia impairs secondary hemostasis, producing deep joint and muscle bleeds. Platelet and von Willebrand defects cause petechiae and mucosal bleeding.
A patient has calf pain when the foot is dorsiflexed (Homans' sign). Which test best rules out DVT when negative?
D-dimer is a fibrin degradation product with a high negative predictive value: a normal result in low-risk patients makes DVT unlikely. Homans' sign itself is unreliable.
Which coagulation result is expected in hemophilia A?
Factor VIII is in the intrinsic pathway, so APTT is prolonged while PT, platelet count and platelet function are normal. Abnormal ristocetin aggregation suggests von Willebrand disease.