In heparin-induced thrombocytopenia (HIT), is there immunological memory? Do patients with a history of HIT have higher risk of developing HIT with subsequent exposure to heparin?

No. For patients who have received heparin in the last 100 days, thrombocytopenia can develop rapidly (median = 10.5 hours), due to circulating PF4/H antibodies. However, patients who are re-exposed to the drug months to years after antibody disappearance do not manifest anamnestic responses, and seroconversion risk appears similar to de novo heparin exposure.