Q: What is spontaneous HIT?

 Answer: When Heparin Induced Thrombocytopenia (HIT) occurs without heparin exposure is called spontaneous HIT. Risk factors are preceding infectious or inflammatory events, or orthopedic surgery. Spontaneous HIT is defined as: "otherwise unexplained thrombocytopenia/thrombosis without proximate heparin exposure and with anti-PF4/heparin IgG antibodies that cause strong in vitro platelet activation even in the absence of heparin"


Reference: 

1. Warkentin TE, Basciano PA, Knopman J, Bernstein RA. Spontaneous heparin-induced thrombocytopenia syndrome: 2 new cases and a proposal for defining this disorder. Blood 2014; 123:3651.

2. Mallik A, Carlson KB, DeSancho MT. A patient with 'spontaneous' heparin-induced thrombocytopenia and thrombosis after undergoing knee replacement. Blood Coagul Fibrinolysis 2011; 22:73. 

3. Pongas G, Dasgupta SK, Thiagarajan P. Antiplatelet factor 4/heparin antibodies in patients with gram negative bacteremia. Thromb Res 2013; 132:217.