MLT GlobeHematology: Hemostasis & coagulation – page 7
125 Hematology MCQs on Hemostasis & coagulation with answers and explanations.
A patient with AL amyloidosis has an isolated low factor X with prolonged PT and aPTT, and no inhibitor. The mechanism is:
Amyloid fibrils bind factor X and remove it from the circulation, a known acquired factor X deficiency. Vitamin K deficiency lowers II, VII, IX and X together.
A patient with lifelong bleeding has low factor VIII (15%) but normal VWF antigen and ristocetin cofactor. Father and mother both have mild symptoms. Which test best separates type 2N vWD from mild hemophilia A?
Type 2N VWF cannot bind and protect factor VIII, so VIII is low despite normal VWF levels; the VWF:FVIIIB assay shows this. Its autosomal pattern also differs from X-linked hemophilia.
VWF multimer analysis shows loss of high- and intermediate-molecular-weight multimers, low VWF activity/antigen ratio, and no enhanced response to low-dose ristocetin. The vWD type is:
Type 2A lacks large multimers and has low function relative to antigen. Type 2B also loses large multimers but shows increased low-dose ristocetin response; type 2M has normal multimers.
A thromboelastography (TEG) tracing from a bleeding surgical patient shows a normal R time but a very low maximum amplitude (MA). This mainly suggests:
R time reflects time to initial fibrin (clotting factors, heparin effect), while MA reflects clot strength, which depends mainly on platelets and fibrinogen. Heparin prolongs the R time.
Unlike the other coagulation factors, factor VIII is produced mainly by:
Factor VIII is made mainly by liver sinusoidal endothelial cells (and other endothelium), not hepatocytes. This is one reason factor VIII is normal or high in liver disease while hepatocyte-made factors fall.