Refractory delayed-onset heparin induced thrombocytopenia (HIT) without thrombosis, treated with intravenous immunoglobulin.

Heparin-induced thrombocytopenia (HIT) is a platelet activation syndrome characterized by the sudden onset of thrombocytopenia and/or thrombosis, induced by anti-platelet factor 4 (PF4)/heparin antibodies that cause platelet activation and destruction. Delayed-onset heparin-induced thrombocytopenia is a variant of HIT that occurs in less than 5 % of cases and is characterized by the onset of thrombocytopenia and/or thrombosis several days after heparin discontinuation. With treatment, the platelet count usually recovers within a week, but in up to 1 % of patients, thrombocytopenia persists for several weeks or months, which is referred to as refractory (persisting) HIT. Refractory delayed-onset HIT represents an important clinical entity because of its potential complications as well as the challenges and complexities in diagnostics and treatment. In the following case report, we present a case of a 69-year-old man diagnosed with refractory delayed-onset HIT, confirmed by a functional assay for platelet-activating anti-PF4/heparin antibodies, who prolonged platelet count recovery without evident signs of thrombosis and was successfully treated with intravenous immunoglobulin (IVIG). This case report provides important clinical and laboratory data necessary for the timely recognition, diagnosis, and treatment of refractory delayed-onset HIT. It also emphasizes the need to consider HIT variants and highlights the importance of early recognition and treatment to minimize complications such as thrombosis and bleeding.