Which of the following is a risk factor for heparin‑induced thrombocytopenia (HIT)?

• A. Warfarin therapy for atrial fibrillation
• B. Placental abruption
• C. Systemic lupus erythematosus
• D. Heparin therapy for deep‑vein thrombosis (DVT)

Answer: (D)

HIT occurs when the immune system makes antibodies against the heparin–platelet factor 4 complex, leading to platelet activation, thrombocytopenia, and a high risk of clots. The key risk factor is exposure to heparin, especially unfractionated heparin, so using heparin to treat a deep-vein thrombosis directly sets up the body for HIT. The other options don’t involve heparin exposure and aren’t established risk factors for HIT: warfarin therapy isn’t a HIT trigger (and can complicate management if HIT is present), while placental abruption and systemic lupus erythematosus are not HIT risk factors.