It is anticipated that this data analysis will provide a current overview of the implications of a positive heparin PF-4 antibody test in clinical practice. It should determine the percentage of positive heparin PF-4 antibody tests that are associated with thrombocytopenia and thrombosis (HIT-T) or "isolated" HIT at diagnosis and the subsequent major clinical outcomes of death, limb amputation/gangrene, and new thrombosis. No "snapshot" of such HIT patients has been conducted in the past decade and the results will be important in assessing the impact of HIT in current medical care as well as documenting current treatment strategies.