The presence of HIT antibodies (antibodies to heparin-platelet factor four complex) has been found in multiple studies to confer risk of arterial and venous thrombosis even in the absence of overt thrombocytopenia. Results of these studies along with pathophysiologic mechanisms are discussed in this review in American Heart Journal.
I previously cited a study showing a relationship between antibody positivity and a variety of adverse outcomes in patients undergoing cardiac surgery. Data such as these beg the question of whether patients (those with previous heparin exposure) should be screened for antibodies on a wide scale. The review authors suggest patient selection for antibody testing, but do not believe widespread testing is cost effective.