Platelet factor 4 immune disease: medical emergencies that look like heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) is a serious adverse reaction to heparin. Other HIT-like syndromes are increasingly recognised, mediated by antibodies binding to platelet factor 4, with or without identifiable polyanions. The history of heparin exposure is atypical for classical HIT and standard HIT laboratory tests may be negative. This manuscript describes subtypes of HIT-like syndromes and highlights practical tips for diagnosis and therapy.