Rosh Internal Medicine Boost Practice Exam

In a patient who has developed thrombocytopenia after being on a heparin drip, what is the most likely diagnosis?

1. Disseminated intravascular coagulation

2. Heparin-induced thrombocytopenia

3. Immune thrombocytopenia

4. Thrombotic thrombocytopenic purpura

The correct answer is: Heparin-induced thrombocytopenia

In patients who develop thrombocytopenia during or after exposure to heparin, the most likely diagnosis is heparin-induced thrombocytopenia (HIT). This condition occurs due to an immune-mediated reaction where antibodies form against complexes of heparin and platelet factor 4 (PF4). This immune response leads to a decrease in platelet count, which can occur 5 to 14 days after starting heparin therapy or more rapidly if the patient has been previously exposed to heparin. HIT is characterized not only by thrombocytopenia but also by the paradoxical risk of thrombosis, which can make it particularly dangerous. Recognizing HIT is crucial for the management and care of the patient, as it requires immediate cessation of heparin and may necessitate the use of alternative anticoagulants. Other conditions listed, such as disseminated intravascular coagulation or immune thrombocytopenia, do not have the same association with heparin administration. Thrombotic thrombocytopenic purpura is also not triggered by heparin but rather is related to a deficiency in ADAMTS13 enzyme activity, leading to excessive clotting and low platelet counts. Understanding these distinctions helps clarify why hepar