Which finding is most characteristic of heparin-induced thrombocytopenia?

Which finding is most characteristic of heparin-induced thrombocytopenia?

• A. Platelet count decreases after heparin exposure
• B. Platelet count increases after heparin exposure
• C. Prolonged PT only
• D. No change in platelets

Answer: (A)

HIT is an immune-mediated reaction where antibodies form against the PF4–heparin complex, causing platelet activation and removal from circulation. This leads to a noticeable drop in the platelet count after heparin exposure, often occurring 5–14 days after starting therapy (and faster if there was recent prior exposure). The hallmark is thrombocytopenia, not an increase in platelets. The condition also carries a paradoxical risk of thrombosis despite low platelets, so the lab finding you’d expect is a decrease in platelets, not a prolonged PT or no change. Therefore, the most characteristic finding is a platelet count that falls after heparin exposure.

HIT is an immune-mediated reaction where antibodies form against the PF4–heparin complex, causing platelet activation and removal from circulation. This leads to a noticeable drop in the platelet count after heparin exposure, often occurring 5–14 days after starting therapy (and faster if there was recent prior exposure). The hallmark is thrombocytopenia, not an increase in platelets. The condition also carries a paradoxical risk of thrombosis despite low platelets, so the lab finding you’d expect is a decrease in platelets, not a prolonged PT or no change. Therefore, the most characteristic finding is a platelet count that falls after heparin exposure.