Overview and Practical Application of Coagulation Assays in Managing Anticoagulation with Direct Oral Anticoagulants (DOACs)

Rapid Determination of Xa Inhibitor Activity in Blood Using a Microfluidic Device that Measures Platelet Deposition and Fibrin Generation Under Flow

Background

Patients taking direct oral anticoagulants (DOACs) often present complicated scenarios following major bleeding, stroke, or emergency surgery. Rapid whole blood assays of DOAC levels would aid clinical decisions such as the need for DOAC reversal.

Methods

We developed a single-use, storage-stable, eight-channel microfluidic device to estimate factor Xa (FXa) inhibitor (apixaban or rivaroxaban) levels in venous thromboembolism or atrial fibrillation patients. The assay simultaneously measured whole blood clotting dynamics on collagen/tissue factor (TF; wall shear rate, 200 -1 ) under four ex vivo conditions: no-treatment control, high dose Factor Xa inhibition, low dose or high dose FXa reversal agent (andexanet alfa). Fibrin and platelet deposition dynamics were monitored via two-color epifluorescence microscopy. Plasma samples were also evaluated by LC-MS/MS for DOAC concentrations.

Results

Experiments with healthy volunteer blood spiked with DOAC verified device performance (DOAC IC 50 ∼120 nM) and confirmed that andexanet alfa added to healthy donor blood had no off-target effect on platelet or fibrin signal. Patient whole blood monitored for 15 to 25 minutes (17 minutes mean runtime) allowed calculation of functional DOAC concentrations ranging from 2 to 500 nM that correlated well with LC-MS/MS determination of apixaban or rivaroxaban (R 2  = 0.7 or 0.9, respectively). Platelet dysfunction was not observed in any patient on DOAC. For a threshold of 100 nM DOAC, the area under the curve (AUC) was found to be 0.881 for apixaban and 0.933 for rivaroxaban.

Conclusion

Microfluidic testing of whole blood can provide a rapid estimate of DOAC levels over the on-therapy range.

Multidisciplinary Expert Guidance for the Management of Severe Bleeding on Oral Anticoagulation: An Algorithm for Practicing Clinicians

Bleeding complications associated with oral anticoagulant (OAC) frequently lead to emergency department visits and hospitalization. Short-term all-cause mortality after severe bleeding is substantial ranging from approximately 10% for gastrointestinal bleeding (the most frequent single site) to approximately 50% for intracranial bleeding. A protocol for multidisciplinary approach to bleeding is needed to (i) ensure rapid identification of patients at risk of adverse outcomes, (ii) optimize delivery of supportive measures, (iii) treat the source of bleeding, and (iv) administer anticoagulant reversal or hemostatic therapies judiciously for patients most likely to benefit. We convened a multidisciplinary panel of experts (emergency medicine, gastroenterology, general internal medicine, hematology, neurology, pharmacy, thrombosis) to review the literature and provide practical guidance including a corresponding algorithm for use at the point of care to assist clinicians in the management of patients with acute severe OAC-related bleeding.

DOACs: role of anti-Xa and drug level monitoring

Direct oral anticoagulants (DOACs) do not require routine monitoring of anticoagulant effect, but measuring DOAC activity may be desirable in specific circumstances to detect whether clinically significant DOAC levels are present (eg, prior to urgent surgery) or to assess whether drug levels are excessively high or excessively low in at-risk patients (eg, after malabsorptive gastrointestinal surgery). Routine coagulation tests, including the international normalized ratio (INR) or activated partial thromboplastin time (aPTT), cannot accurately quantify drug levels but may provide a qualitative assessment of DOAC activity when considering the estimated time to drug clearance based on timing of last drug ingestion and renal and hepatic function. Drug-specific chromogenic and clot-based assays can quantify drug levels but they are not universally available and do not have established therapeutic ranges. In this review, we discuss our approach to measuring DOAC drug levels, including patient selection, interpretation of coagulation testing, and how measurement may inform clinical decision-making in specific scenarios.

International Council for Standardization in Haematology Guidance for New Lot Verification of Coagulation Reagents, Calibrators, and Controls

The clinical laboratory uses commercial products with limited shelf life or certain expiry dates requiring frequent lot changes. Prior to implementation for clinical use, laboratories should determine the performance of the new reagent lot to ensure that there is no significant shift in reagent performance or reporting of patient data. This guideline has been written on behalf of the International Council for Standardization in Haematology (ICSH) to provide the framework and provisional guidance for clinical laboratories for evaluating and verifying the performance of new lot reagents used for coagulation testing. These ICSH Working Party consensus recommendations are based on good laboratory practice, regulatory recommendations, evidence emerged from scientific publications, and expert opinion and are meant to supplement regional standards, regulations, or requirements.

Efficacy and safety of direct oral anticoagulants versus warfarin in the treatment of cerebral venous sinus thrombosis

BACKGROUND

Given the evolving application and promising outcomes of direct oral anticoagulants (DOACs) in various thromboembolic conditions, we aimed to compare the efficacy and safety of DOACs with warfarin in the post-acute treatment of cerebral venous sinus thrombosis (CVST) using clinical and radiological parameters.

METHODS

A total of 140 CVST patients were enrolled, with 95 receiving warfarin and 45 receiving DOACs as post-acute treatment. Clinical and imaging parameters of the patients in follow-up visits were investigated, including the last modified Rankin Scale (mRS), venous thromboembolic events, CVST recurrence, mortality rate, recanalization status, and hemorrhagic events, to compare the efficacy and safety of treatment between the two groups.

RESULTS

At baseline, patients' assessments using two prognostic scores, ISCVT-RS and IN-REvASC, revealed that there was no statistically significant difference in the distribution of prognostic risk categories between the warfarin and DOACs groups. Following acute therapy, patients in the warfarin and DOACs groups were followed up for the median of 359 and 325 days, respectively. Analysis to compare the efficacy of warfarin and DOACs revealed no significant difference in last mRS scores, CVST recurrence rate, venous thromboembolic events, and recanalization status between the two groups. Additionally, there was no statistically significant difference in the risk of hemorrhagic events between warfarin and DOACs groups.

CONCLUSION

Our findings show that DOACs have comparable safety and efficacy in the post-acute treatment of CVST patients; however, large-scale randomized controlled trials are required to validate our findings.

Assessing Direct Oral Anticoagulants in the Clinical Laboratory

Direct oral anticoagulants (DOACs) have significant advantages over vitamin K antagonists including lack of need for routine laboratory monitoring. However, assessment of DOAC effect and concentration may be important to guide clinical management including need for DOAC reversal, particularly in acute or emergent situations. In this manuscript, the authors describe tests to screen for DOAC presence and tests that have demonstrated equivalence to gold standard testing for quantifying DOAC exposure. They also discuss the effect of DOACs on other coagulation assays and strategies for monitoring unfractionated heparin in patients with concomitant DOAC exposure.

The myths behind DOAC measurement: Analyses of prescribing information from different regulatory bodies and a call for harmonization

For more than a decade, US laboratories have failed to implement solutions to help their clinicians in managing complex situations or patients on direct oral anticoagulants (DOACs). The problem may find different origins, among which is the position of the Food and Drug Administration, which categorized these drugs as monitoring- and measurement-free, whereas other regulatory bodies like the European Medicines Agency or the Therapeutic Goods Administration in Australia were more conservative on the principle that the absence of proof (of monitoring/measurement benefits) is not proof of an absence (of monitoring/measurement needs). Pivotal clinical studies that led to the approval of DOACs were presented as devoid of such testing, although some companies considered monitoring as a solution to improve their benefit/risk ratio. In this JTH In Clinics issue, we report more than a decade of development that has permitted the activation of smart laboratory solutions to qualify or quantify DOACs and discuss myths and misconceptions around technical and regulatory requirements that support the current reluctance of implementing these technologies in most US laboratories. Use of DOACs is ever expanding, with DOAC prescriptions now exceeding those of other anticoagulants, including vitamin K antagonists, in some geographies. As this use increases, the likely need to measure DOAC exposure will also increase. Measurement of DOACs does not represent any technical difficulty. That these laboratory tests are not available in some locations suggests disparities in patient care, and we suggest it is time to address such inequalities.

A Review of Direct-acting Oral Anticoagulants and Their Use in Solid Organ Transplantation

Direct-acting oral anticoagulant (DOAC) use has increased dramatically since their introduction because of the growing evidence of proven efficacy and enhanced safety compared with warfarin and the low-molecular-weight heparins in the general population. Unfortunately, there is a dearth of quality data regarding the safety and efficacy of the DOACs in patients awaiting organ transplant and those who received a solid organ transplant. This review aims to evaluate the available literature and considerations regarding anticoagulation use in transplant recipients, focusing on preoperative, perioperative, and postoperative DOAC use.

Using a low-molecular weight heparin-calibrated anti-factor Xa assay to assess the concentration of apixaban and rivaroxaban

INTRODUCTION

Direct oral anticoagulant (DOAC)-inhibiting factor Xa (FXa-DOAC) are being increasingly used as prophylaxis of venous thromboembolism and for prevention of stroke in patients with atrial fibrillation. In contrast to vitamin K antagonists, DOACs do not require monitoring in general. However, it is sometimes of value in the acute setting, for instance when considering a reversal agent in uncontrolled bleeding in patients on DOAC.

METHODS

We evaluated if a low-molecular weight heparin (LMWH)-calibrated anti-factor Xa assay could be used to estimate FXa-DOAC concentration in the concentration range <100 ng/mL by spiking known concentrations of FXa-DOAC and from those result calculate the FXa-DOAC concentration from the response of the LMWH assay. This procedure was then evaluated by comparing the result with a drug-calibrated chromogenic assay and liquid chromatography tandem mass spectrometry (LC-MS/MS) on clinical plasma samples from patients treated with apixaban or rivaroxaban.

RESULTS

Although the measuring range was narrower for the LMWH-calibrated assay, concentrations recalculated from the LMWH assay was comparable with those measured by the drug-calibrated method when compared with LC-MS/MS.

CONCLUSION

We suggest that an LMWH-calibrated anti-factor Xa assay can be used after characterization of the response of FXa-DOACs to give guidance on the concentration of apixaban and rivaroxaban. Shorter turnaround time than LC-MS/MS and the greater availability than drug-calibrated chromogenic assays could make this a valuable option in the acute setting.

Review of coagulation preanalytical variables with update on the effect of direct oral anticoagulants

There are many preanalytical variables (PAV) that are known to affect coagulation testing. The more commonly acknowledged PAV addressed by the clinical laboratory tend to start with their influence on blood collection, but realistically coagulation PAV starts with the patient, where the laboratory has less influence or control. Patient selection and appropriate timing for blood collection may be integral for assuring proper diagnosis and management. Laboratory control and assurance for ideal phlebotomy practice would mitigate most PAVs related to blood collection to minimize suboptimal sample collection. Laboratory oversight of sample transportation, processing and storage will assure sample integrity until testing can be facilitated. The purpose of this document is to review common PAV that should be taken into consideration when ordering, performing and interpreting a coagulation test result, with additional attention to the effect of direct oral anticoagulants (DOACs).

2021 Update of the International Council for Standardization in Haematology Recommendations for Laboratory Measurement of Direct Oral Anticoagulants

In 2018, the International Council for Standardization in Haematology (ICSH) published a consensus document providing guidance for laboratories on measuring direct oral anticoagulants (DOACs). Since that publication, several significant changes related to DOACs have occurred, including the approval of a new DOAC by the Food and Drug Administration, betrixaban, and a specific DOAC reversal agent intended for use when the reversal of anticoagulation with apixaban or rivaroxaban is needed due to life-threatening or uncontrolled bleeding, andexanet alfa. In addition, this ICSH Working Party recognized areas where additional information was warranted, including patient population considerations and updates in point-of-care testing. The information in this manuscript supplements our previous ICSH DOAC laboratory guidance document. The recommendations provided are based on (1) information from peer-reviewed publications about laboratory measurement of DOACs, (2) contributing author's personal experience/expert opinion and (3) good laboratory practice.