OBJECTIVES: Heparin-induced thrombocytopenia (HIT) is a life-threatening complication of heparin therapy. At our institution, postoperative cardiac surgical patients are screened for HIT antibodies, when platelet counts persist to be less than 50% of the baseline level or less than 50000 nl(-1). In the present study, we compared the outcomes in HIT-antibody-positive and HIT-antibody-negative patients.METHODS: Patients who underwent a cardiac surgical procedure between 1999 and 2007 and in whom a clinical suspicion of HIT prompted a test for heparin-dependent platelet-activating antibodies, that is, the heparin-induced platelet activation (HIPA) test, were retrieved from the database. Patients were divided in group 1 (antibodies present) and group 2 (no antibodies present).RESULTS: In 153 of more than 10000 patients (1.5%), a HIPA test was performed, Of those, 21 patients tested positive (group 1) and 132 tested negative (group 2). Central venous and pulmonary thrombo-embolism was more frequent in group 1 (10% vs 2%, p=0.04). Intestinal, microvascular thrombo-embolism was more frequent in group 2 (15% as opposed to 0%, p=0.03). By multivariate analysis, only patient age (p=0.04, confidence interval (CI): 1.04 (1.00-1.08)), female sex (p=0.03 CI 3.45 (1.51-7.86)) and perioperative sepsis (p<0.001 CI 6.88 (2.96-16.02)) were associated with mortality.CONCLUSION: Patients in whom a low platelet count prompted testing for HIT antibodies, had a high mortality (59%), independent of whether heparin-dependent antibodies were present, indicating that a persistently lowered platelet count is a bad prognostic sign after cardiac surgery. Interestingly, the HIPA-positive patients had more central venous and pulmonary embolisms. Patient age, female sex and perioperative sepsis were risk factors for perioperative mortality.