Table 1.

Five autoimmune HIT (aHIT) disorders.

Name of aHIT Disorder	Concept (Definition)
Delayed-onset HIT	Platelet count fall that begins or worsens despite stopping heparin
Persisting (refractory) HIT	Delayed platelet count recovery despite stopping heparin (>1 week)
Heparin “flush” HIT	HIT that occurs with exposure only to small amounts of heparin
Fondaparinux-induced HIT	HIT associated with proximate exposure to fondaparinux
Unusually severe HIT	Marked thrombocytopenia, multiple-site thromboses, overt DIC, etc.

Abbreviations: aHIT, autoimmune heparin-induced thrombocytopenia; DIC, disseminated intravascular coagulation; HIT, heparin-induced thrombocytopenia.