Abstract 13410: Diagnosing Heparin Induced Thrombocytopenia Post Cardiac Surgery
Thrombocytopenia (Tcp) is common post cardiac surgery (CS) and may be due to heparin induced thrombocytopenia (HIT). HIT has a high rate of thrombosis necessitating anticoagulation with a non-heparin anticoagulant. Inappropriate anticoagulation for HIT can lead to bleeding/tamponade. Incorrect diagnosis of HIT can lead to morbidity, mortality, and litigation. HIT ELISAs report a positive (pos) or negative (neg) value or an optical density (OD) value. The gold standard to diagnose HIT is a serotonin release assay (SRA) which is done in limited centers. Scoring systems to help diagnose HIT include the 4T score (J Thromb Haemost 2006; 4: 759), with a score of ≥4 being an intermediate risk for HIT and the cardiopulmonary bypass (CPB) score (J Thromb Haemost 2004; 2: 1882), with a score of ≥2 being a high risk for HIT. We sought to determine the ability of the scoring systems and the ELISA to diagnose HIT in reference to the SRA in patients with tcp post-CS.
Methods: Patients (n=150) were scored using the two systems, and 132 of these with a “pos” HIT ELISA were categorized based on the ELISA OD reading and the SRA values.
Results: Table 1 shows that higher ELISA readings, generally predict higher SRA values; however, there are patients with high ELISA OD readings that did not have high SRA (test is very sensitive). Also, a “pos” ELISA (which all the patients had) does not equate to a high SRA (a high OD generally equates to high SRA). The two scoring systems (Tables 2a/b) were not accurate in predicting HIT but were better at predicting who did not have HIT (specific with high negative predictive value).
Conclusions: The ELISA is sensitive and the scoring systems are specific. ELISAs that provide OD values (rather than a dichotomous pos or neg) should be used. If the ELISA OD is high, then the SRA is likely to be high, justifying the risks of starting a non-reversible, possibly expensive, non-heparin anticoagulant on a patient at reasonable risk for bleeding/tamponade.
- © 2013 by American Heart Association, Inc.