His clinical work and related research focuses on acquired thrombocytopenias and coagulopathies—most notably the topics of “heparin-induced thrombocytopenia (HIT)” and "ischemic limb gangrene with pulses" (symmetrical peripheral gangrene/purpura fulminans associated with critical illness). Dr. Warkentin devised the “4Ts”, a widely-used scoring system for evaluating clinical probability of HIT. He is a co-winner (with Prof. John Kelton) of the 2015 Prix Galien Canada Prize, the highest award for Canadian scientists who have made significant advances in pharmaceutical research.

He also identified “spontaneous HIT syndrome” (a rare HIT-mimicking disorder that occurs despite absence of preceding heparin exposure), and other examples of “autoimmune HIT”—a group of unusual clotting disorders that provides insight into “vaccine-induced immune thrombotic thrombocytopenia (VITT),” a novel prothrombotic anti-PF4 platelet-activating disorder that rarely is caused by adenoviral vector vaccines.