The occurrence of HIT varies widely between clinical populations and is dependent on the type of heparin used, i.e. UFH vs. LMWH. The highest incidence reported to date has been in the cardiac and orthopedic populations and is unknown in the ICU population. Warkentin, et al found in a study of 655 hip surgery patients that 2.7% randomized to UFH developed HIT while none receiving enoxaparin (LMWH) developed HIT. This variability in development of antibodies and the HIT syndrome makes it critically important to understand heparin induced antibody formation as a precursor to HIT and HITT.