(1007) Impact of HemosIL HIT Antibody Test Adoption on Argatroban and Fondaparinux Prescribing Patterns

Introduction: Heparin-induced thrombocytopenia (HIT) results from autoantibodies against platelet factor 4 (PF4) in complex with heparin, causing platelet activation and a prothrombotic state. The HemosIL anti-PF4 test is a qualitative, latex-enhanced immunoassay (LIA) with improved specificity compared to the enzyme-linked immunoassay (ELISA). However, there are few studies on how these tests affect anticoagulation management. Argatroban and fondaparinux (ARGAT-FONDA) are used for HIT treatment. The objective of this study was to compare the duration of ARGAT-FONDA therapy before and after implementing the LIA.

Methods: This IRB-approved retrospective review included adult patients (≥ 18 years) with an anti-PF4 test result from 3/2020-5/2021 (ELISA group) or 7/2021-9/2022 (LIA group) who received ARGAT-FONDA Exclusion criteria were positive SRA results, treatment for presumed HIT, transfer from another hospital on ARGAT-FONDA vaccine-induced immune thrombotic thrombocytopenia, pregnancy, or incarceration. The primary outcome was duration of ARGAT-FONDA while secondary outcomes included incidence of positive anti-PF4 tests, defined by the manufacturer thresholds, and major or clinically relevant minor bleeding events, defined by the International Society on Thrombosis and Haemostasis criteria. Continuous variables were analyzed using the Wilcoxon rank-sum test, and categorical variables with Chi-square or Fisher’s exact test. Multivariate logistic regression identified factors associated with positive anti-PF4 results.

Results: Out of 149 patients screened, 83 were included. There were no significant differences in the duration of ARGAT-FONDA between the ELISA and LIA groups (median 54.4 vs. 47.0 hours, p=0.49), or in the rates of positive anti-PF4 tests (24% vs. 12%, p=0.26). Major bleeding events occurred in two ELISA patients and one LIA patient (p=0.66), and two minor bleeding events were observed only in the ELISA group (p=0.20). Multivariate analysis identified weight as a predictor of positive anti-PF4 results (OR 1.04, 95% CI 1.00-1.06).

Conclusions: There was no significant reduction in ARGAT-FONDA duration or in the incidence of positive anti-PF4 tests or bleeding events after LIA implementation.