A-159 A Digital Microfluidic Approach to Accurate Heparin Monitoring in DOAC-Treated Patients

Abstract Background Direct oral anticoagulants (DOACs) are widely prescribed for atrial fibrillation (AF) and venous thromboembolism (VTE). Patients on DOACs may need to transition to heparin during hospital admission for surgical procedures or when rapid reversal of anticoagulation is desired. However, the presence of residual DOACs is known to interfere with anti-Factor Xa (aFXa) assays resulting in overestimation of aFXa activity and potentially delaying the initiation of heparin therapy and critical interventions. Such artificial inflation may result in suboptimal anticoagulation management or unwarranted deferral of urgent procedures. We investigated a digital microfluidic (DMF) method to measure heparin without interference from common DOACs . We focused on scenarios where patients may still have circulating DOAC levels beyond a presumed washout period, yet require timely heparin administration. Preliminary data suggest that the DMF aFXa assay is unaffected by remnant apixaban. Our objective was to substantiate these findings through analytical and clinical method comparison against conventional assays. Methods Remnant citrated whole blood samples were obtained from patients (IRB–approved protocol) who had aFXa ordered as part of their clinical care. Four samples were collected from individuals with remnant apixaban more than 48 hours after the last dose, and 56 samples were confirmed as without any DOAC exposure. For analytical interference studies, pooled normal whole blood was spiked with unfractionated heparin at 0.50 IU/mL and apixaban or rivaroxaban at 0, 100, and 200 ng/mL. These concentrations were chosen because, for AF and VTE patients on 2.5 mg apixaban and 20 mg rivaroxaban, even the trough plasma values span 34-162 ng/mL and 4-96 ng/mL, respectively. All samples were tested on a DMF aFXa assay and an FDA-cleared comparator (chromogenic assay on plasma from centrifugation). For the DMF method, 50 µL of whole blood was separated into plasma using agglutination within the cartridge, from which a 1 µL plasma droplet is dispensed and mixed with a droplet containing preloaded reagents (FXa and fluorogenic substrate). Fluorescence is inversely proportional to the concentration of heparin in the sample. Total assay time is under 14 minutes. Results were analyzed using correlation and weighted Deming regression to assess equivalence and interference. Results In the analytical interference study, DMF anti-FXa measurements remained essentially unchanged with apixaban (0.50-0.52 IU/mL) or with rivaroxaban (0.44-0.51 IU/mL) spiked at 0–200 ng/mL, while the comparator assay values increased three to fivefold from baseline. A similar pattern emerged in four clinical samples from patients with remnant apixaban, where comparator values (0.46–1.92 IU/mL) were significantly higher than DMF (0.14–0.45 IU/mL). By contrast, in 56 patient specimens without any DOAC exposure, DMF correlated strongly with the comparator (R = 0.89; slope = 0.95), confirming assay equivalence in the absence of DOAC interference. Conclusion Conventional aFXa test results had a significant positive bias in the presence of DOACs, while DMF method results remained unaffected. Accurate heparin measurement under such circumstances is crucial for timely clinical decisions. This novel approach could enhance anticoagulation management in patients transitioning from DOACs to unfractionated heparin. Further clinical studies are underway to establish clinical performance.