Which of the Following Is True About Heparin-Induced Thrombocytopenia (HIT)

Which of the following is true about heparin-induced thrombocytopenia (HIT) ?

A) It is heralded by a sudden unexplained decrease in platelets on the first day of heparin therapy.
B) Because HIT patients are thrombocytopenic, they are all at high risk for bleeding complications.
C) It appears to be caused by an immune response related to heparin exposure.
D) If a patient did not develop HIT the first time he or she was ever exposed to heparin, then he or she has no risk of developing HIT on subsequent exposures to heparin.
E) All of the above