Prevalence of Heparin Antibodies in ICU Patients (The HAICU Study).

BACKGROUND: Heparin-induced thrombocytopenia (HIT) is an antibody-mediated prothrombotic disorder characterized by absolute or relative thrombocytopenia occurring after exposure to heparin. Although thrombocytopenia in HIT patients usually resolves after discontinuing heparin, the risk for thrombosis persists up to 3 months.

PURPOSE: The HAICU study was conducted to determine the prevalence of heparin-induced antibodies and HIT on admission to the intensive care unit (ICU) and their development within a week of hospitalization.

METHODS: Platelet counts and heparin-platelet factor 4 antibodies (GTI ELISA) were measured on admission and again on day 7 ± 2 or discharge on a convenience sample of ICU patients. Patients with new onset thrombocytopenia (unexplained platelet count <100 x10⁹/L or a 50% decrease in count) or a positive ELISA had confirmatory testing for HIT antibodies using a serotonin release assay. HIT was prospectively defined as positive HIT antibodies by both assays or as HIT antibodies with new onset, unexplained thrombocytopenia.

RESULTS: Over 6 months, 118 patients were enrolled from three ICUs. Subjects had an average ICU LOS of 9 +/− 11 days, hospital LOS of 20 +/− 11 days and Apache II Physiology Score of 14 +/− 7; 59% were male. HIT, as defined above, occurred in 3 (3%) patients on admission. After 7.2 ± 2 days, HIT occurred in an additional 9 patients. Overall, 12 of 118 (10%) ICU patients had HIT at or within a week of admission (Table 1). 5 had documented prior exposure to heparin within 100 days of ICU admission, and 4 received heparin during the period when HIT assays were performed. Cases were distributed throughout the ICU’s, yet relatively more often in the neurotrauma and shock-trauma units than the medical unit.

CONCLUSION: Heparin-induced antibodies and HIT are common in the ICU, occurring in 3% of patients on admission and 10% in the first week. Physicians need to be aware of heparin exposure and the possibility of HIT in this population.