Heparin induced thrombocytopenia (HIT) involves the development of antibodies against platelets in response to exposure to heparin.
These heparin induced antibodies specifically target a protein on the platelets called platelet factor 4 (PF4). These are anti-PF4/heparin antibodies.
The HIT antibodies bind to platelets and activate clotting mechanisms. This causes a hypercoagulable state and leads to thrombosis. They also break down platelets and cause thrombocytopenia. Therefore there is an unintuitive situation where a patient on heparin with low platelets forms unexpected blood clots.
Diagnosis is by testing for the HIT antibodies in the patients blood.
Management is by stopping heparin and using an alternative anticoagulant guided by a specialist.