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SPLTRAK Abstract Submission
Analysis of Heparin-induced thrombocytopenia (HIT) testing and implementation of electronic record based calculation of 4T score
Hannah L McRae1, Rialnat Lawal2, Mofiyin Obadina2, Frank Akwaa3, Majed Refaai1,3
1Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY, United States/2Department of Medicine, University of Rochester Medical Center, Rochester, NY, United States/3Department of Medicine, Division of Hematology/Oncology, Rochester, NY, United States

Background: Heparin-induced thrombocytopenia (HIT) is an antibody-mediated adverse reaction to heparin therapy. The reported incidence of HIT is between 0.5-5% in patients receiving unfractionated heparin. Given the prevalence of heparin administration in the hospital and recent reports of over diagnosis of HIT, we hypothesize that HIT is over-tested at our institution, where the PF4 IgG assay (Immucor, Inc., Peachtree Corners, GA) is used. To effectively screen for HIT, the determination of the pretest probability (4T score) is recommended by the American Society of Hematology (ASH). Therefore, on January 1, 2019 we implemented an electronic version of the 4T score calculator into the electronic medical record (EMR) ordering system. We suspect that the high ratio of negative to positive HIT tests is a lapse in the adequate calculation of the 4T score.    Objectives: To determine if the implementation of the 4T score calculator into our test ordering system affected the proportion of HIT tests ordered at our institution.     Methods: We performed a retrospective analysis of HIT testing and pretest probability data from January 2018 through December 2019, before and after implementation of an electronic 4T score calculator into our test ordering system.     Results: The proportion of negative (82%) and positive (18%) was unchanged from 2018 to 2019; however, there was a 19% decline in the total number of tests ordered in 2019 (from 334 tests in 2018 to 270 tests in 2019). Of the HIT tests that were ordered in 2019, 181 (67%) received a score of 4-5 (intermediate probability) by the ordering provider, of which 30 (17%) resulted positive. In addition, 58 (21%) received a score of 6-8 (high probability), of which only 14 (24%) resulted positive (Figure).     Conclusions: According to the ASH 4T score model, a score of 4-5 has a probability of approximately 14% of HIT, while the probability for a score of 6-8 is approximately 64%. For our institution, in patients who are assigned a high probability score, there appears to be a large difference between the rate of positive and negative HIT results. This discrepancy is likely secondary to miscalculation of the 4T score that stems from an insufficient understanding of its application by providers, which leads to inappropriate HIT testing. As a result, we can conclude that the implementation of the 4T score calculator in the EMR alone was not sufficient to mitigate the over-testing of HIT at our center. Thus, we are developing several initiatives to aid in provider/trainee education at our center starting in January 2020 with the goal of decreasing the total number of HIT tests performed, as well as ensuring accurate and thorough 4T score calculation by the ordering providers.