American Association of Veterinary State Boards (AAVSB) Practice Exam 2026 - Free AAVSB Practice Questions and Study Guide

Prolonged PT or PTT points to a problem in the coagulation cascade, not in the platelets. PT tests the extrinsic and common pathways, while PTT tests the intrinsic and common pathways. When these times are extended, it usually means there’s a deficiency or inhibition of the vitamin K–dependent clotting factors II, VII, IX, and X. Anticoagulant rodenticide exposure causes exactly that by blocking vitamin K recycling, leading to reduced activity of those factors and, consequently, prolonged PT and/or PTT. That’s why rodenticide poisoning fits best. Von Willebrand disease mainly affects platelet function (and can mildly affect PTT via FVIII, but not via the extrinsic pathway), whereas thrombocytopenia and thrombocytopathy primarily involve platelets and often don’t prolong PT/PTT.