Heparin-induced thrombocytopenia
| Generally refers to the immune-mediated syndrome | |
|---|---|
| Etiology | Antibody to PF4/heparin complex (forms +ve feedback loop) |
| Epidemiology | Incidence: 1-5% with UFH; <1% with LMWH |
| Clinical presentation | 5-10 days after heparin 4T scoring - pre-test probability: - thrombocytopenia severity - timing of onset - thrombosis - thrombocytopenia from other causes? |
| Pathogenesis | IgG binding to PF4/heparin complex → clustering of platelet Fc-receptors = platelet activation = thrombosis HIT antibodies binding to Fc receptors on monocytes Endothelial damage - ↑ vWF |
| Diagnostic investigations | Tets only if pre-test probability is high! - ELISA/antigen assay PF4/polyanion - functional assays (only if ELISA equivocal and 4T high) - HIPA, serotonin release |
| Management | Stop heparin - don't forget heplocks and catheters! Avoid platelet ransfusion Find alternatives e.g. Factor Xa inhibitors - fondaparinux Avoid warfarin until platelet count recovered due to risk of skin necrosis |
Normally, PF4 released on platelet activation - after trauma, inflammation, cancer, surgery
Effect - inhibits formation of megakaryocytes, angiogenesis