Monitoring the Effects of Direct Oral Anticoagulants with a Novel Point-of-Care Sensor: Results of a Pilot Clinical Study

Introduction:Direct oral anticoagulants (DOACs) are a new class of medications that have been designed to provide direct inhibition of either coagulation factor IIa (FIIa, dabigatran) or FXa (rivaroxaban, apixaban, and edoxaban) and are rapidly replacing warfarin as the anticoagulant-of-choice for the treatment of most thrombotic disorders and atrial fibrillation. These newer agents present several advantages including predictable pharmacokinetic profile, wide therapeutic window, and shorter half-life. Despite these advantages, metabolism of DOACs is complex and requires enteric absorption and liver or renal clearance. Thus, the pervading maxim that DOACs do not require laboratory monitoring is simplistic and there are several situations in which assessment of the anticoagulant effect of DOACs will be useful. Indications for assessment of DOAC effects on the coagulation system include need for emergent surgery, unexpected thrombotic or hemorrhagic events, patients with extreme body weight, abrupt impairment of liver and kidney function, suspicion of DOAC overdose, poor compliance, or after administration of reversal agents. To date, no assays developed to measure DOAC activity have been approved by the Food and Drug Administration (FDA). Thus, there is an unmet need for a rapid coagulation assay that can measure the anticoagulant effect of DOACs in the laboratory or at the POC. We have recently developed a novel dielectric microsensor, termed ClotChip, that allows for the comprehensive assessment of blood hemostasis using a disposable microfluidic sensor at the POC (Fig 1A). The aim of this study was to assess the clinical utility of ClotChip at measuring the anticoagulant effects of DOACs in whole blood.

Methods: We conducted a pilot clinical study at the Louis Stokes Cleveland VA Medical Center and accrued 127 individuals after IRB approval. Of these, 47 were healthy volunteers (not taking any anticoagulation or antiplatelet therapy) and the remaining participants were patients on DOACs (rivaroxaban: n=25, apixaban: n=47, dabigatran: n=8). Whole blood samples were collected in 3.2% sodium citrate. Samples from patients on DOACs were collected within 6 hours of rivaroxaban ingestion, between 3 - 5 hours post-morning dose of apixaban, or within 12 hours of dabigatran intake. All samples underwent whole blood measurement with ClotChip within 4 hours of collection as well as conventional plasma-based coagulation tests including PT, aPTT, drug specific anti-Xa assays or dilute thrombin time. The ClotChip is based on the electrical technique of dielectric spectroscopy (DS) to monitor the hemostatic process ex vivo in a low-cost (material cost < $1), small-sized (26mm × 9mm × 3mm), and disposable microfluidic sensor with miniscule sample volume (< 10µL). The ClotChip readout was taken as the temporal variation in the real part of blood dielectric permittivity at 1 MHz. The time to reach a peak in permittivity (T_peak), is a sensitive parameter to assess coagulation defects, and we hypothesized that T_peakcan effectively measure the anticoagulant effect of DOACs (Fig. 1B).

Results:Using Gaussian fit method, mean T_peakfor the control group was determined to be 429 sec (239 - 619 sec, ±2 SD, Fig 1C). There was statistically significant prolongation in T_peakfor rivaroxaban (637 ± 24 sec., mean ± SEM, p < 0.0001), apixaban (593 ± 23 sec, mean ± SEM, p < 0.0001) and dabigatran (894 ± 82 sec, mean ± SEM, p < 0.0001) samples (Fig 1C). An ROC curve was then generated using statistical software to determine the true positive rate (sensitivity) and false positive rate (100% - specificity). The area under the curve (AUC) for ClotChip T_peakwas 0.9185 for rivaroxaban, 0.8132 for apixaban and 1 for dabigatran (Fig 1D).

Conclusions:There are currently no approved laboratory assays that reliably measure the anticoagulant effect of DOACs. ClotChip offers a portable POC platform for rapid, comprehensive assessment of hemostasis using a miniscule amount of whole blood (<10 µL). In this pilot study, ClotChip showed excellent sensitivity at detecting the anticoagulant effects of DOACs. A larger clinical trial is currently being planned to validate these results and help establish ClotChip as a reliable method to detect and monitor DOAC activity.

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