Assuming a constant infusion of intravenous heparin at steady-state, administration of which of the following will SHORTEN the partial thromboplastin time (PTT):
a) FFP
b) Antithrombin III
c) Vitamin K
d) A and B
e) None of the above
Answer e. Vitamin K administration does not generally affect the intrinsic coagulation pathway, and thus does not change the PTT. In contrast, fresh frozen plasma and antithrombin III administration provide additional substrate for heparin anticoagulation (which functions via potentiation of antithrombin), and result in a paradoxical prolongation of the PTT.