Revisiting the Use of Unfractionated Heparin As VTE Prophylaxis: A Single Institution, Retrospective Review
Authors: Dhaliwal Armaan , Siu Chun , Lillestolen Derek , Zaffiri Kathryn , Lash Bradley W. 
Published: December 2024

Introduction
Hospital-acquired deep vein thrombosis (DVT) and pulmonary embolism (PE) occur in approximately 1.3% and 0.4% of admissions, respectively, in the United States. The 2018 ASH Clinical Practice Guidelines emphasize the preference for low molecular weight heparin (LMWH) over unfractionated heparin (UFH) for venous thromboembolism (VTE) prophylaxis during hospitalization due to its once-daily administration and lower complication rates, including a reduced risk of heparin-induced thrombocytopenia (HIT). Historically, HIT affects between 0.04% and 3% of patients exposed to heparin or its derivatives. However, we hypothesized that UFH is favored at our institution due to its shorter half-life and consequently, there could be a higher incidence of HIT. This study aims to examine the incidence of heparin product usage and associated type 2 immune-mediated HIT at our institution.
Methods
Our study is a retrospective analysis of anticoagulation use at a large tertiary care teaching hospital from July 1, 2021, to June 30, 2024. We included a total of 82,299 adult patients admitted, comprising 121,734 hospitalizations over three years. Hospitalizations were evenly distributed across these years. We evaluated orders for various anticoagulation medications, including prophylactic and therapeutic use. To evaluate and compare unfractionated heparin use at our institution, we accessed the Vizient database to analyze its incidence nationwide.
This study examines the incidence of HIT at our institution and associated heparin-based anticoagulation use. According to ASH guidelines, we attributed HIT responsibility to the type of anticoagulation initiated 5-14 days before HIT testing. Our institution uses heparin-associated platelet antibodies (HAPA) as a screening test, with confirmation by serotonin release assay (SRA). All confirmed HIT cases showed a positive SRA result.
Results
Over the three-year period, Vizient report ranked our institution as one of the top 35 institution in unfractionated heparin usage when compared to over 300 other institutions across the nation. From our retrospective review, a total of 56,161 UFH orders were placed including 47,421 prophylactic and 8,740 therapeutic doses, which accounts for 46% of all anticoagulation orders. LMWH was ordered in 25,534 hospitalizations (21%), with 21,937 for prophylactic and 3,597 for therapeutic purposes.
A total of 566 patients were suspected of having HIT, leading to 623 HIT orders consisting of HAPA with reflex to SRA. Among these patients, 44 SRA orders were positive, and 35 patients were confirmed to have HIT, indicating that only 6.18% of suspected HIT patients had a confirmed HIT diagnosis. Overall, 0.04% of the 81,695 hospitalizations exposed to heparin and its derivatives were diagnosed with HIT. Notably, none of the HIT cases occurred with LMWH, with one case identified as spontaneous HIT. Of the confirmed HIT cases, 24 (68.5%) were associated with therapeutic UFH and 10 (28.5%) with prophylactic UFH.
Conclusion
Despite high usage of unfractionated heparin at our institution, when compared to other institutions across the country, the incidence of HIT remains rare. Most HIT cases were associated with the use of UFH, with more than a quarter of the cases involving prophylactic UFH alone and over half involving therapeutic UFH. Our study highlights the need to reevaluate UFH use in both prophylactic and therapeutic settings and to consider other anticoagulation alternatives to decrease HIT incidence. Our next step is a quality improvement initiative to disseminate these findings across different specialties within our institution and to better understand ordering preferences for VTE prophylaxis.