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A1879 - “HIT or Miss”: Approaching Heparin Induced Thrombocytopenia (HIT) in an Academic Hospital System
Author Block: I. Kourouni1, S. Peeke2, M. Varma3, I. Shapira2, J. M. Shapiro1; 1Pulmonary Critical Care and Sleep Medicine, Mount Sinai St. Luke's West, New York, NY, United States, 2Hematology Oncology, Mount Sinai Beth Israel Hospital Center, New York, NY, United States, 3Hematology Oncology, Mount Sinai St. Luke's West, New York, NY, United States.
RATIONALE: HIT is a rare clinical entity that combines thrombocytopenia with thrombogenicity and imposes significant morbidity if missed. The diagnosis requires clinical suspicion with laboratory testing with PF4Ab ELISA(PF4) and Serotonin Release Assay(SRA). The decision to treat critically ill thrombocytopenic patients with an alternative anticoagulant carries clinical and potentially medicolegal risks. We performed a quality improvement project to review the approach to suspected HIT. METHODS:We retrospectively reviewed all adult inpatients tested for HIT at three teaching hospitals of our hospital system, during the 2-year period 2012-2014. Cases were identified from Laboratory Department. The pre-test (based on “4T”score, often retrospective) and post-test clinical probability of HIT was reviewed with Hematology specialists for each HIT case. RESULTS:Laboratory testing for HIT was performed in 494 patients. Testing included:PF4 in 84(17%), SRA in 182(36%), both in 228(46%), with average result time of 3 days. Erroneous testing (anti-Xa) was performed in 67(13%). Most tests 300/495(60%) were performed for ICU patients. The assays yielded indeterminate results in 94/494(19%) cases. Ultimately 15/494(3%) were diagnosed with HIT by clinical and laboratory data. Of the 15 HIT+ cases, 12/15(80%) were ICU patients, and 3/15(20%) were stepdown patients with recent ICU course or major orthopedic procedure. In our cohort, 152/494(30%) patients with retrospective low 4T had SRA sent. Out of the HIT-positive cases, 4T score was high in 4/15, intermediate in 11/15, and low in none. DIC was tested in only 168/494(34%) prior to HIT testing. Management of suspected cases was not standardized: heparin was continued in 88/494(17%) and discontinued without alternative anticoagulant in 358/494(72%). 77HIT negative patients received alternative anticoagulation. Hematology consultations were obtained in 147/245(60%) of cases at one site compared to 45/249(18%) at the other two. Hematology involvement was associated with greater use of anticoagulation for suspected HIT: 62/245(25%) vs 26/249(10%). CONCLUSION: Our results demonstrate significant oversuspicion of HIT, and unreliable performance of the 4T test for intermediate 4T-score in critically ill. We found remarkable heterogeneity in management within the three hospitals. HIT suspicion overshadowed other causes of thrombocytopenia in ICU including sepsis-related DIC. Initial PF4 testing and subsequent SRA if warranted, is not efficient in institutions that do not result same day PF4 testing. An EMR HIT order-set with correct testing and 4T documentation could improve diagnostic testing. Intensivists need to weigh the extremely low incidence of HIT in their consultations with hematologists in making the decision to anticoagulate critically ill patients with intermediate 4T.