Platelet Factor IV (PF4) is a 70 aa protein released from the alpha granules of activated platelets. PF4 is synthesized by bone marrow megakaryocytes and stored in alpha granules as a non-covalent bound tetramer. Platelet factor IV binds with high affinity to heparin and plays a role in inflammation and wound repair. PF4 is a chemoattractant for neutrophils, monocytes and fibroblasts and has been reported to be an immunologic regulator that inhibits suppressor T-cell activity. Heparin-Induced Thrombocytopenia/Thrombosis (HIT/HITT) is a life-threatening complication that manifests itself in a small population of patients exposed to intravenous-heparin. It is characterized by the production of PF4/heparin auto-antibodies. These auto-antibodies bind the PF4/heparin complexes and subsequently bind the FCGIIa receptor on the platelets surface through their Fc region. This activates the platelets and can initiate clot formation.