1019

Abstract

Introduction: Given the multitude of thrombocytopenia etiologies in critically ill patients, the diagnosis of heparin-induced thrombocytopenia (HIT) in the intensive care unit (ICU) is often difficult to make. The purpose of this study is to determine if a modified scoring system impacts diagnostic accuracy. Hypothesis: We hypothesized that a modified 3T (m3T) scoring system, which omits clinical evaluation of other thrombocytopenic etiologies, is as effective for the clinical diagnosis of HIT in the ICU when compared to the 4T score. Methods: This was a retrospective cohort analysis of critically ill adults who had an enzyme-linked immunosorbent assay HIT antibody (ELISA HIT Ab) ordered and were identified as HIT positive (optical density [OD]? 0.40) or HIT negative (OD < 0.40) based on the ELISA HIT Ab. Both 4T and m3T scores were retrospectively calculated for patients and the diagnostic accuracy was compared using paired receiver operating characteristic curves (ROC). The number of HIT positive to HIT negative patients was represented by a 1:3 ratio to detect at least a 10% difference in the areas under the ROC curves (AUC) for the 4T and m3T scores. Results: A total of 1487 adult ICU patients with an ELISA HIT Ab ordered between January 2007 and December 2009 were eligible for study enrollment. Application of either exclusion criteria or random selection yielded a total of 232 patients included for analysis (58 HIT positive patients and 174 HIT negative). The majority patients were admitted into surgical ICUs and were primarily exposed to unfractionated heparin. Patients that were HIT positive had a median OD value of 0.61 (IQR 0.47 – 0.92), whereas the median OD value was 0.07 (IQR 0.05 – 0.11) in HIT negative patients (p < 0.001). The AUC for the 4T and m3T scores were 0.683 (95% confidence interval [CI], 0.604-0.762) and 0.680 (95% CI, 0.600-0.758), respectively (p = 0.065). Conclusions: There was no significant difference between the 4T and m3T scoring systems for the diagnosis of HIT in critically ill patients. Further prospective studies should be conducted to validate the m3T scoring system.