Point-of-Care Testing of Coagulation in Patients Treated With Non-Vitamin K Antagonist Oral Anticoagulants

Detection of factor Xa activity using giant magnetoresistive biosensors

BACKGROUND

As anticoagulants are widely used to treat patients with atrial fibrillation (AF) and other thrombotic conditions, it is necessary for physicians to determine whether the medication has been taken in emergencies. Among many anticoagulants, rivaroxaban has attracted attention due to its safety and convenience. Since rivaroxaban inhibits activated coagulation factor X (factor Xa), measuring factor Xa activity can determine the presence of rivaroxaban.

RESULTS

We report a magnetic biosensing platform capable of measuring the activity of factor Xa using peptide substrates conjugated with magnetic nanoparticles (MNPs). Due to the size of factor Xa, a new method of solution-phase assays was proposed for magnetic biosensing platforms to address issues with immobilized peptides on the sensors. This method was validated with factor Xa and trypsin, both of which are serine proteases. In the solution-phase assays, samples with either the enzymes of interest or no enzyme were simultaneously measured, and the activity of the enzyme was estimated using the difference between the measurements. Unlike conventional optical methods, our platform was capable of detecting the activity of factor Xa at 2 μg mL-1 with a 30 min sample incubation.

SIGNIFICANCE

The assay using giant magnetoresistive biosensors outperformed conventional optical techniques. This platform can facilitate the determination of the presence of rivaroxaban and assist physicians in deciding on appropriate treatments for patients.

Assessing mortality and safety of IV thrombolysis in ischemic stroke patients on direct oral anticoagulants (DOACs): A systematic review and meta-analysis

BACKGROUND

Intravenous thrombolysis (IVT) is considered a standard reperfusion therapy for acute ischemic stroke (AIS) patients presenting within 4.5 hours of the last known well (LKW). Current guidelines contraindicate the use of IVT in patients within the window who are on Direct Oral Anticoagulants (DOACs) and took their last dose within 48 hours of presentation, due to a risk of symptomatic intracranial hemorrhage (sICH).

OBJECTIVE

To assess the safety of IVT as management of AIS in patients who take DOACs.

METHODS

A thorough literature search of four databases (PubMed, Scopus, Medline, Google Scholar, Web of science and ScienceDirect) was done from inception until May 2023. Double-arm studies that reported outcomes of mortality, sICH, and mRS scores were selected. Results from these studies were presented as odds ratios (ORs) with 95 % confidence intervals (CIs) and were pooled using a random-effects model.

RESULTS

Four eligible studies were included with a total of 238,425 stroke patients who underwent IVT (3330 in the DOAC arm and 235,217 in the placebo arm). The group with prior DOAC intake showed a significant decrease in sICH development and an increase in functional independence at 90 days compared to the control group. No significant association was seen between prior DOAC use and any serious alteplase-related complication within 36 hours, serious systemic or life-threatening hemorrhage within 36 hours, mortality within 3 months, or mRS score at 3 months.

CONCLUSION

The pooled analysis suggests that IVT is a safe management option for acute ischemic stroke in patients with DOAC intake before symptom onset without an increased risk of serious adverse events.

Electrochemical Monitoring in Anticoagulation Therapy

The process of blood coagulation, wherein circulating blood transforms into a clot in response to an internal or external injury, is a critical physiological mechanism. Monitoring this coagulation process is vital to ensure that blood clotting neither occurs too rapidly nor too slowly. Anticoagulants, a category of medications designed to prevent and treat blood clots, require meticulous monitoring to optimise dosage, enhance clinical outcomes, and minimise adverse effects. This review article delves into the various stages of blood coagulation, explores commonly used anticoagulants and their targets within the coagulation enzyme system, and emphasises the electrochemical methods employed in anticoagulant testing. Electrochemical sensors for anticoagulant monitoring are categorised into two types. The first type focuses on assays measuring thrombin activity via electrochemical techniques. The second type involves modified electrode surfaces that either directly measure the redox behaviours of anticoagulants or monitor the responses of standard redox probes in the presence of these drugs. This review comprehensively lists different electrode compositions and their detection and quantification limits. Additionally, it discusses the potential of employing a universal calibration plot to replace individual drug-specific calibrations. The presented insights are anticipated to significantly contribute to the sensor community's efforts in this field.

Hemoclot Thrombin Inhibitor Assay and Expected Peak-Trough Levels of Dabigatran: A Multicenter Study

Purpose

Dabigatran concentrations monitoring are gaining importance of special situations, but limited data are available for the expected peak and trough levels. The hemoclot thrombin inhibitor (HTI) is dabigatran-calibrated quantitative determination of dabigatran concentration. This study aims to validate HTI assay as the quantification choice of dabigatran, and providing the expected peak and trough levels.

Materials and Methods

This is a multi-center methodology validate study, including seven hospitals from Beijing, Shanghai, Henan, Hunan, Chongqing, and Fujian. We retrospectively analyzed plasma samples taken from 118 healthy subjects and 183 patients receiving dabigatran. Dabigatran concentrations were measured with HTI assay and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Linear regression, Spearman correlation and Bland-Altman analysis were used in this study.

Results

The mean concentration ratio of HPLC-MS/MS and HTI assays was 1.03 and 0.98 at 2 and 12 h, and the acceptance ranges for both the ratio limit as well as the limit of agreement were met, suggesting good agreement between the HTI-derived plasma concentrations and HPLC-MS/MS. The reference detection range of single dose dabigatran 150 mg in healthy subjects was 33–159 ng/ml. About 500 blood samples were taken from 183 patients suggested that the expected peak and trough levels range of dabigatran 110 mg was about 95–196 and 36–92 ng/ml.

Conclusion

Hemoclot thrombin inhibitor assay can be a good quantitative detection method of dabigatran. Expected peak and trough levels provide a basis for the rational use of dabigatran, and provide important Asian population data for the update of the international clinical guidelines for hematological testing.

Clinical Trial Registration

[https://clinicaltrials.gov], identifier [NCT03161496].

Acute Stroke and Atrial Fibrillation: Risk of Incorrect NOAC Dosage When Estimating Renal Function From Plasma Creatinine Only

Background

Cardioembolic stroke (CS) due to atrial fibrillation (AF) bears a high risk of unfavorable outcome. Treatment with a non-vitamin K antagonist oral anticoagulant (NOAC) reduces this risk. NOAC dosage occurs on a thin line during the acute phase of the stroke unit when the patient is threatened by both recurrent CS and a hemorrhagic stroke. It is often adapted to renal function—usually glomerular filtration rate (GFR)—to prevent both under- and overdosing. This study investigates the hypothetical risk of incorrect NOAC dosage after acute stroke when relying on plasma creatinine alone in comparison to a more exact renal function assessment including urine collection.

Methods

In a cohort study on consecutive 481 patients treated in a stroke unit with acute stroke and AF, the GFR estimated from plasma creatinine (eGFR) was compared to concurrent creatinine clearance measurement (CrCl) from urine collection regarding the hypothetically derived NOAC dosage.

Results

The risk of incorrect dosage (mean, 95% confidence interval) was 6.9% (4.8–9.5), 26% (23–31), 38% (33–42), and 20% (16–23) for apixaban, dabigatran, edoxaban, and rivaroxaban, respectively. The overall risk for incorrect dosage of any NOAC was 23% (21–25). Thresholds for age and admission eGFR were optimized to achieve an overall risk below 5% by additional CrCl measurements in selected patients (apixaban <36 ml/min and any age, dabigatran <75 ml/min and >70 y, edoxaban >36 ml/min and >58 y, rivaroxaban <76 ml/min and >75 y, any NOAC <81 ml/min and >54 y). The resulting portion of patients requiring an additional CrCl measurement was 10, 60, 80, 55, and 65% for apixaban, dabigatran, edoxaban, rivaroxaban, and any NOAC, respectively.

Conclusions

There is a considerable risk of incorrect NOAC dosage in patients with acute CS treated in a stroke unit that can be lowered by targeted CrCl measurements in selected patients.

Accuracy of a Single, Heparin-Calibrated Anti-Xa Assay for the Measurement of Rivaroxaban, Apixaban, and Edoxaban Drug Concentrations: A Prospective Cross-Sectional Study

Background

Applying a single anti-Xa assay, calibrated to unfractionated heparin to measure rivaroxaban, apixaban, and edoxaban would simplify laboratory procedures and save healthcare costs.

Aim

We hypothesized that a heparin-calibrated anti-Xa assay would accurately measure rivaroxaban, apixaban, and edoxaban drug concentrations and correctly predict clinically relevant drug levels.

Methods

This analysis is part of the Simple-Xa study, a prospective multicenter cross-sectional study conducted in clinical practice. Patients treated with rivaroxaban, apixaban, or edoxaban were included. Anti-Xa activity was measured using the Siemens INNOVANCE^® Heparin assay. Drug concentrations were determined using ultra-high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cut-off levels were determined in a derivation dataset (50% of patients) and sensitivities and specificities were calculated in a verification dataset (50% of patients).

Results

Overall, 845 patients were available for analysis. Correlation coefficients (r _s ) between the heparin-calibrated anti-Xa assay and drug concentrations were 0.97 (95% CI 0.97, 0.98) for rivaroxaban, 0.96 (0.96, 0.97) for apixaban, and 0.96 (0.94, 0.99) for edoxaban. The area under the receiver operating characteristics curve (ROC) was 0.99 for all clinically relevant drug concentrations. In the verification dataset, the sensitivity was 94.2% (95% CI 90.8-96.6) for 30 μg L^-1, 95.8% (92.4-98.0) for 50 μg L^-1, and 98.7% (95.5-99.9) for 100 μg L^-1. Specificities were 86.3% (79.2-91.7), 89.8% (84.5-93.7), and 88.7% (84.2-92.2), respectively.

Conclusion

In a large prospective study in clinical practice, a strong correlation of heparin-calibrated anti-Xa measurements with LC-MS/MS results was observed and clinically relevant drug concentrations were predicted correctly.

Diagnostic Modalities in Critical Care: Point-of-Care Approach

The concept of intensive care units (ICU) has existed for almost 70 years, with outstanding development progress in the last decades. Multidisciplinary care of critically ill patients has become an integral part of every modern health care system, ensuing improved care and reduced mortality. Early recognition of severe medical and surgical illnesses, advanced prehospital care and organized immediate care in trauma centres led to a rise of ICU patients. Due to the underlying disease and its need for complex mechanical support for monitoring and treatment, it is often necessary to facilitate bed-side diagnostics. Immediate diagnostics are essential for a successful treatment of life threatening conditions, early recognition of complications and good quality of care. Management of ICU patients is incomprehensible without continuous and sophisticated monitoring, bedside ultrasonography, diverse radiologic diagnostics, blood gas analysis, coagulation and blood management, laboratory and other point-of-care (POC) diagnostic modalities. Moreover, in the time of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, particular attention is given to the POC diagnostic techniques due to additional concerns related to the risk of infection transmission, patient and healthcare workers safety and potential adverse events due to patient relocation. This review summarizes the most actual information on possible diagnostic modalities in critical care, with a special focus on the importance of point-of-care approach in the laboratory monitoring and imaging procedures.

Acute Stroke Treatment in an Anticoagulated Patient: When Is Thrombolysis an Option?

Purpose of Review

Direct oral anticoagulants (DOACs: the factor Xa inhibitors rivaroxaban, apixaban, and edoxaban and the direct thrombin inhibitor dabigatran) are the mainstay of stroke prevention in patients with non-valvular atrial fibrillation (AF). Nevertheless, there is a residual stroke risk of 1–2% per year despite DOAC therapy. Intravenous thrombolysis (IVT) reduces morbidity in patients with ischemic stroke and improves functional outcome. Prior DOAC therapy is a (relative) contraindication for IVT but emerging evidence supports its use in selected patients.

Recent Findings

Recent observational studies highlighted that IVT in patients on prior DOAC therapy seems feasible and did not yield major safety issues. Different selection criteria and approaches have been studied including selection by DOAC plasma levels, non-specific coagulation assays, time since last intake, and prior reversal agent use. The optimal selection process is however not clear and most studies comprised few patients.

Summary

IVT in patients taking DOAC is a clinically challenging scenario. Several approaches have been proposed without major safety issues but current evidence is weak. A patient-oriented approach balancing potential benefits of IVT (i.e., amount of salvageable penumbra) against expected bleeding risk including appropriate monitoring of anticoagulant activity seem justified.

Point-of-care testing of coagulation in patients treated with edoxaban

Edoxaban, alongside other direct oral anticoagulants (DOAC), is increasingly used for prevention of thromboembolism, including stroke. Despite DOAC therapy, however, annual stroke rate in patients with atrial fibrillation remains 1–2%. Rapid exclusion of relevant anticoagulation is necessary to guide thrombolysis or reversal therapy but, so far, no data exists on the effect of edoxaban on available point-of-care test systems (POCT). To complete our previous investigation on global coagulation-POCT for the detection of DOAC, we evaluated whether CoaguChek®-INR (CC-INR) is capable of safely ruling out edoxaban concentrations above the current treatment thresholds of 30/50 ng/mL in a blood sample. We studied patients receiving a first dose of edoxaban; excluding subjects receiving other anticoagulants. Six blood samples were collected from each patient: before drug intake, 0.5, 1, 2 and 8 h after intake, and at trough (24 h). CC-INR and mass spectrometry for edoxaban concentrations were performed for each time-point. One hundred and twenty blood samples from 20 patients contained 0–302 ng/mL of edoxaban. CC-INR ranged from 0.9 to 2.3. Pearson’s correlation coefficient showed strong correlation between CC-INR and edoxaban concentrations (r = 0.73, p < 0.001). Edoxaban concentrations > 30 and > 50 ng/mL were ruled out by CC-INR ≤ 1.0 and ≤ 1.1, respectively, with high specificity (> 95%), and a sensitivity of 44% (95%-confidence interval: 30–59%) and 86% (74–93%), respectively. Our study represents the first evaluation of coagulation-POCT in edoxaban-treated patients. CC-POCT is suitable to safely exclude clinically relevant edoxaban concentrations prior to thrombolysis, or guide reversal therapy in stroke patients.

Recanalisation therapies for acute ischaemic stroke in patients on direct oral anticoagulants

Direct oral anticoagulants (DOACs) have emerged as primary therapeutic option for stroke prevention in patients with atrial fibrillation. However, patients may have ischaemic stroke despite DOAC therapy and there is uncertainty whether those patients can safely receive intravenous thrombolysis or mechanical thrombectomy. In this review, we summarise and discuss current knowledge about different approaches to select patient. Time since last DOAC intake-as a surrogate for anticoagulant activity-is easy to use but limited by interindividual variability of drug pharmacokinetics and long cut-offs (>48 hours). Measuring anticoagulant activity using drug-specific coagulation assays showed promising safety results. Large proportion of patients at low anticoagulant activity seem to be potentially treatable but there remains uncertainty about exact safe cut-off values and limited assay availability. The use of specific reversal agents (ie, idarucizumab or andexanet alfa) prior to thrombolysis is a new emerging option with first data reporting safety but issues including health economics need to be elucidated. Mechanical thrombectomy appears to be safe without any specific selection criteria applied. In patients on DOAC therapy with large vessel occlusion, decision for intravenous thrombolysis should not delay thrombectomy (eg, direct thrombectomy or immediate transfer to a thrombectomy-capable centre recommended). Precision medicine using a tailored approach combining clinicoradiological information (ie, penumbra and vessel status), anticoagulant activity and use of specific reversal agents only if necessary seems a reasonable choice.

Coagulation Assay and Stroke Severity upon Admission of Patients with Cardioembolic Cerebral Infarction during Direct Oral Anticoagulant Use

Although the severity of acute cerebral infarction varies in patients receiving direct oral anticoagulants (DOACs), no practical method to predict the severity has been established. We analyzed retrospectively the relationship between cardioembolic cerebral infarction severity and coagulation indicators in patients treated with DOACs. We assessed the anticoagulation effect of DOACs using the activated partial thromboplastin time (APTT), prothrombin time (PT), and prothrombin time international standardized ratio (PT-INR) in 71 patients with cardioembolic cerebral infarction admitted to our hospital between January 2015 and December 2019. The participants were divided into a prolongation group (prolonged APTT for oral thrombin inhibitors or prolonged PT for oral factor Xa inhibitors, n =37) and a normal group (no prolongation of coagulation markers, n =34). Of the 71 patients, 21 (30%) and 50 (70%) were using oral thrombin and oral factor Xa inhibitors, respectively. PT, PT-INR, and APTT were significantly higher in the prolongation group (PT: 17.4 ± 5.1 vs. 12.8 ± 1.4 s, P < 0.001; PT-INR: 1.5 ± 0.5 vs. 1.1 ± 0.1, P < 0.001; APTT: 44.8 ± 26.4 vs. 30.4 ± 4.1 s, P = 0.003). The median National Institutes of Health Stroke Scale (NIHSS) score on admission and the prevalence of large vessel occlusion were significantly lower in the prolongation group (NIHSS: 2.0 vs. 9.5, P = 0.007; large vessel occlusion: 27% vs. 53%, P = 0.031). The prevalence of large vessel occlusion was low and stroke severity was mild in patients undergoing DOAC therapy with prolongation of coagulation assay markers upon onset of cardioembolic cerebral infarction.

Point-of-care testing for emergency assessment of coagulation in patients treated with direct oral anticoagulants including edoxaban

BACKGROUND

Direct oral anticoagulants (DOAC) including edoxaban are increasingly used for stroke prevention in atrial fibrillation. Despite treatment, annual stroke rate in these patients remains 1-2%. Rapid assessment of coagulation would be useful to guide thrombolysis or reversal therapy in this growing population of DOAC/edoxaban-treated stroke patients. Employing the Hemochron™ Signature Elite point-of-care test system (HC-POCT), clinically relevant plasma concentrations of dabigatran and rivaroxaban can be excluded in a blood sample. However, no data exists on the effect of edoxaban on HC-POCT results. We evaluated whether edoxaban plasma concentrations above the current treatment thresholds for thrombolysis or anticoagulation reversal (i.e., 30 and 50 ng/mL) can be ruled out with the HC-POCT.

METHODS

We prospectively studied patients receiving a first dose of edoxaban. Six blood samples were collected from each patient: before, 0.5, 1, 2, 8, and 24 h after drug intake. HC-POCT-based INR (HC-INR), activated clotting time (HC-ACT+ and HC-ACT-LR), activated partial thromboplastin time (HC-aPTT), and mass spectrometry for edoxaban plasma concentrations were performed at each time-point. We calculated correlations, receiver operating characteristics (ROC) and test-specific cut-offs for ruling out edoxaban concentrations > 30 and > 50 ng/mL in a blood sample.

RESULTS

One hundred twenty blood samples from 20 edoxaban-treated patients were analyzed. Edoxaban plasma concentrations ranged from 0 to 512 ng/mL. HC-INR/HC-ACT+/HC-ACT-LR/HC-aPTT ranged from 0.7-8.3/78-310 s/65-215 s/19-93 s, and Pearson's correlation coefficients showed moderate to very strong correlations with edoxaban concentrations (r = 0.95/0.79/0.70/0.60). With areas under the ROC curve of 0.997 (95% confidence interval: 0.991-0.971) and 0.989 (0.975-1.000), HC-INR most reliably ruled out edoxaban concentrations > 30 and > 50 ng/mL, respectively, and HC-INR results ≤1.5 and ≤ 2.1 provided specificity/sensitivity of 98.6% (91.2-99.9)/98.0% (88.0-99.9) and 96.8% (88.0-99.4)/96.5% (86.8-99.4).

CONCLUSIONS

Our study represents the first systematic evaluation of the HC-POCT in edoxaban-treated patients. Applying sufficiently low assay-specific cut-offs, the HC-POCT may not only be used to reliably rule out dabigatran and rivaroxaban, but also very low edoxaban concentrations in a blood sample. Because the assay-specific cut-offs were retrospectively defined, further investigation is warranted.

TRIAL REGISTRATION

ClinicalTrials.gov, registration number: NCT02825394 , registered on: 07/07/2016, URL.

Specific Point-of-Care Testing of Coagulation in Patients Treated with Dabigatran

BACKGROUND AND PURPOSE

 Accurate and rapid assessment of coagulation status is necessary to guide thrombolysis or reversal of anticoagulation in stroke patients, but commercially available point-of-care (POC) assays are not suited for coagulation testing in patients treated with direct oral anticoagulants (DOACs). We aimed to evaluate the direct thrombin monitoring (DTM) test card by Helena Laboratories (Texas, United States) for anti-IIa-specific POC coagulation testing, hypothesizing that its POC-ecarin clotting time (POC-ECT) accurately reflects dabigatran plasma concentrations.

METHODS

 A prospective single-center diagnostic study (ClinicalTrials.gov-identifier: NCT02825394) was conducted enrolling patients receiving a first dose of dabigatran and patients already on dabigatran treatment. Blood samples were collected before drug intake and 0.5, 1, 2, 8, and 12 hours after intake. POC-ECT was performed using whole blood (WB), citrated blood (CB), and citrated plasma (CP). Dabigatran plasma concentrations were determined by mass spectrometry.

RESULTS

 In total, 240 blood samples from 40 patients contained 0 to 275 ng/mL of dabigatran. POC-ECT with WB/CB/CP ranged from 20 to 186/184/316 seconds. Pearson's correlation coefficient showed a strong correlation between dabigatran concentrations and POC-ECT with WB/CB/CP (R2  = 0.78/0.90/0.92). Dabigatran concentrations >30 and >50 ng/mL (thresholds for thrombolysis, surgery, and reversal therapy according to clinical guidelines) were detected by POC-ECT with WB/CB/CP (>36/35/45 and >43/45/59 seconds) with 95/97/97 and 96/98/97% sensitivity, and 81/87/94 and 74/60/91% specificity.

CONCLUSION

 This first study evaluating DOAC-specific POC coagulation testing revealed an excellent correlation of POC-ECT with actual dabigatran concentrations. Detecting clinically relevant dabigatran levels with high sensitivity/specificity, the DTM assay represents a suitable diagnostic tool in acute stroke, hemorrhage, and urgent surgery.

Non-vitamin K antagonist oral anticoagulants for stroke prevention in atrial fibrillation: safety issues in the elderly

INTRODUCTION

Non-vitamin K antagonist oral anticoagulants (NOACs) are increasingly used for stroke prevention in patients with atrial fibrillation (AF). Since NOACs are predominantly used in the elderly with AF at high risk for stroke and bleeding and with comorbidities requiring polypharmacy, it is important to assess their safety and efficacy in this population.

AREAS COVERED

We review changes in pharmacokinetics and pharmacodynamics observed with senescence and the effect on NOACs and drug and food interactions. We also provide an update on challenges related to NOAC use in situations that increases the risk for bleeding or require temporary discontinuation and address practical issues in the elderly AF patients managed on NOACs. Clinical studies and trials with cardiovascular outcomes reported from January 1990 to August 2020 were identified through the Medline database using PubMed, Cochrane Library, and EMBASE database.

EXPERT OPINION

NOACs are highly effective in preventing stroke in AF patients with non-inferior or superior efficacy to warfarin, with reduced risk of major bleeding. However, in the older-elderly, evidence comes mainly from observational studies or extrapolation from studies in populations with minimal functional limitations or comorbidities. The high upfront cost and out-of-pocket expense for copayment or deductibles also limit the use of this effective therapy in a substantial number of patients. The cost reduction may further improve long-term use for NOACs in stroke prevention in elderly patients with AF.

Diagnostic performance of coagulation indices for direct oral anticoagulant concentration

INTRODUCTION

Different coagulation indices for direct oral anticoagulants (DOACs) exist in clinical practice, but limited data are available for the diagnostic power of these indices. This review and meta-analysis aims to explore the diagnostic value of coagulation indices for DOACs.

MATERIALS AND METHODS

PubMed, Web of Science, EMBASE, Clinical Trials.gov, and the Cochrane Library were searched from inception of each database to 15 February 2020. Studies reporting a relationship between coagulation indices and the gold standard (liquid chromatography/tandem mass spectrometry) were included in the analysis.

RESULTS

Sixteen articles from 9169 citations evaluating the performance of coagulation indices were included in this review. A total of 236, 273, 273 rivaroxaban samples were included to assess the diagnostic power of anti-Xa activity (AXA), prothrombin time (PT), combined PT and activated partial thromboplastin time, respectively. A total of 268 dabigatran samples were included to assess the diagnostic performance of diluted thromboplastin time (dTT). AXA calibrated by rivaroxaban showed a sensitivity of 0.98 (95% confidence interval (CI): 0.91-0.99) and a specificity of 0.98 (95% CI: 0.94-0.99) at the threshold of 30 ng/mL. For dabigatran, the combined sensitivity of dTT was 0.76 (95% CI: 0.66-0.84) and combined specificity was 0.97 (95% CI: 0.92-0.99).

CONCLUSIONS

DOAC-specific calibrated AXA was a good index to indicate concentration for rivaroxaban and apixaban. More studies on edoxaban and betrixaban are in need. Diluted TT, thrombin inhibitor assay, and ecarin-based assays were potential to measure dabigatran concentration. Due to the limited data, results should be validated in the future.

An Update on the Reversal of Non-Vitamin K Antagonist Oral Anticoagulants

Non-vitamin K antagonist oral anticoagulants (NOACs) include thrombin inhibitor dabigatran and coagulation factor Xa inhibitors rivaroxaban, apixaban, edoxaban, and betrixaban. NOACs have several benefits over warfarin, including faster time to the achieve effect, rapid onset of action, fewer documented food and drug interactions, lack of need for routine INR monitoring, and improved patient satisfaction. Local hemostatic measures, supportive care, and withholding the next NOAC dose are usually sufficient to achieve hemostasis among patients presenting with minor bleeding. The administration of reversal agents should be considered in patients on NOAC's with major bleeding manifestations (life-threatening bleeding, or major uncontrolled bleeding), or those who require rapid anticoagulant reversal for an emergent surgical procedure. The Food and Drug Administration (FDA) has approved two reversal agents for NOACs: idarucizumab for dabigatran and andexanet alfa for apixaban and rivaroxaban. The American College of Cardiology (ACC), American Heart Association (AHA), and Heart Rhythm Society (HRS) have released an updated guideline for the management of patients with atrial fibrillation that provides indications for the use of these reversal agents. In addition, the final results of the ANNEXA-4 study that evaluated the efficacy and safety of andexanet alfa were recently published. Several agents are in different phases of clinical trials, and among them, ciraparantag has shown promising results. However, their higher cost and limited availability remains a concern. Here, we provide a brief review of the available reversal agents for NOACs (nonspecific and specific), recent updates on reversal strategies, lab parameters (including point-of-care tests), NOAC resumption, and agents in development.

Limitations of Specific Coagulation Tests for Direct Oral Anticoagulants: A Critical Analysis

Background

During treatment with direct oral anticoagulants (DOAC), coagulation assessment is required before thrombolysis, surgery, and if anticoagulation reversal is evaluated. Limited data support the accuracy of DOAC‐specific coagulation assays around the current safe‐for‐treatment threshold of 30 ng/mL.

Methods and Results

In 481 samples obtained from 96 patients enrolled at a single center, DOAC concentrations were measured using Hemoclot direct thrombin inhibitor assay, Biophen direct thrombin inhibitor assay or ecarin clotting time for dabigatran, chromogenic anti‐Xa assay (AXA) for factor Xa inhibitors (rivaroxaban, apixaban) and ultraperformance liquid chromatography–tandem mass spectrometry as reference. All dabigatran‐specific assays had high sensitivity to concentrations >30 ng/mL, but specificity was lower for Hemoclot direct thrombin inhibitor assay (78.2%) than for Biophen direct thrombin inhibitor assay (98.9%) and ecarin clotting time (94.6%). AXA provided high sensitivity and specificity for rivaroxaban, but low sensitivity for apixaban (73.8%; concentrations up to 82 ng/mL were misclassified as <30 ng/mL). If no DOAC‐specific calibration for AXA is available, results 2‐fold above the upper limit of normal indicate relevant rivaroxaban concentrations. For apixaban, all elevated results should raise suspicion of relevant anticoagulation.

Conclusions

DOAC‐specific tests differ considerably in diagnostic performance for concentrations close to the currently accepted safe‐for‐treatment threshold. Compared with Biophen direct thrombin inhibitor assay and ecarin clotting time, limited specificity of Hemoclot direct thrombin inhibitor assay poses a high risk of unnecessary anticoagulation reversal or treatment delays in patients on dabigatran. While AXA accurately detected rivaroxaban, the impact of low apixaban levels on the assay was weak. Hence, AXA results need to be interpreted with extreme caution when used to assess hemostatic function in patients on apixaban.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov. Unique identifiers: NCT02371044, NCT02371070.

Monitoring of low dabigatran concentrations: diagnostic performance at clinically relevant decision thresholds

The direct oral anticoagulant dabigatran does not require therapeutic drug monitoring, however emergency measurements are gaining importance. Current assays feature good performance at intermediate and high dabigatran concentrations but show limited accuracy at low concentrations. This area requires more attention as clinical decision threshold values currently lie at 30 and 50 ng/ml. The objective of the study was to evaluate and compare diagnostic performance of dabigatran assays at these thresholds. Dabigatran concentrations of 293 plasma samples taken from 50 patients were measured with the INNOVANCE direct thrombin inhibitor assay (DTI) from Siemens, the Biophen direct thrombin inhibitor assay (BDTI), the BDTI using a low range calibrator (BDTI-low), the Hemoclot direct thrombin inhibitor assay (HTI) and an ecarin clotting time assay (ECT). Assay results were compared to ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and test characteristics were calculated for thresholds of 30 and 50 ng/ml. DTI, BDTI-low and ECT showed very strong correlation and high agreement with UPLC-MS/MS and an improved determination of low dabigatran concentrations. ROC curve analyses revealed very high accuracy at the 30/50 ng/ml thresholds for DTI (AUC = 0.989/0.995), BDTI-low (AUC = 0.980/0.991) and ECT (AUC = 0.990/0.996) measurements. Sensitivity and specificity in detecting were calculated for DTI (98/92%), BDTI-low (87/95%), ECT (97/96%), BDTI (99/82%) and HTI (86/89%) measurements. Compared to the previously available HTI and BDTI, both novel assays, DTI and BDTI-low, reliably determine low dabigatran plasma concentrations around the clinical decision thresholds with very high sensitivity and specificity.

Diagnostic accuracy of thromboelastometry and its correlation with the HPLC-MS/MS quantification test

The aim of the study was to evaluate the diagnostic accuracy of thromboelastometry for assessing rivaroxaban concentrations. The accuracy of thromboelastometry was compared with the high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method, which is the gold standard for drug plasma monitoring (the reference standard). Forty-six clinically stable patients were treated with 10, 15, or 20 mg of rivaroxaban once daily (OD group) or 15 mg twice a day (BID group) (no particular indication for treatment). Patient samples were collected 2 h after the use of the medication (peak) and 2 h before the next dose (trough). The rivaroxaban plasma concentrations were determined via HPLC-MS/MS, and thromboelastometry was performed using a ROTEM® delta analyzer. There were significant prolongations in clotting time (CT) for the 10, 15, and 20 mg of rivaroxaban treatments in the OD groups. In the 15 mg BID group, the responses at the peak and trough times were similar. At the peak times, there was a positive correlation between the plasma concentration of rivaroxaban and CT (Spearman correlation rho=0.788, P<0.001) and clot formation time (rho=0.784, P<0.001), and a negative correlation for alpha angle (rho=−0.771, P<0.001), amplitude after 5 min (rho=−0.763, P<0.001), and amplitude after 10 min (rho=−0.680, P<0.001). The CT presented higher specificity and sensitivity using the cut-off determined by the receiver characteristics curve. ROTEM has potential as screening tool to measure possible bleeding risk associated with rivaroxaban plasma levels.

Benefits and Pitfalls of Point-of-Care Coagulation Testing for Anticoagulation Management: An ACLPS Critical Review

Objectives

Point-of-care (POC) testing is generally less precise and has higher reagent costs per test than laboratory-based assays. However, POC hemostasis testing can offer significant advantages in particular situations: patient-managed warfarin therapy as well as rapid turnaround time heparin management for intraoperative patients. Of note, POC hemostasis testing is generally approved for the purposes of anticoagulation monitoring and is inferior to laboratory coagulation testing for the diagnosis of congenital or acquired coagulopathy.

Methods

The frequently used POC coagulation instruments for POC international normalized ratio and activated clotting time are reviewed, as well as their typical performance relative to central laboratory testing (where available).

Results

Several cases are discussed that highlight the benefits, as well as pitfalls, of POC coagulation testing.

Conclusions

POC coagulation testing for anticoagulation monitoring offers advantages in particular situations. Clear policies and protocols must be developed to guide proper use of POC versus central laboratory hemostasis testing.

Laboratory measures of coagulation among trauma patients on NOAs: results of the AAST-MIT

Background

Warfarin is associated with poor outcomes after trauma, an effect correlated with elevations in the international normalized ratio (INR). In contrast, the novel oral anticoagulants (NOAs) have no validated laboratory measure to quantify coagulopathy. We sought to determine if use of NOAs was associated with elevated activated partial thromboplastin time (aPTT) or INR levels among trauma patients or increased clotting times on thromboelastography (TEG).

Methods

This was a post-hoc analysis of a prospective observational study across 16 trauma centers. Patients on dabigatran, rivaroxaban, or apixaban were included. Laboratory data were collected at admission and after reversal. Admission labs were compared between medication groups. Traditional measures of coagulopathy were compared with TEG results using Spearman's rank coefficient for correlation. Labs before and after reversal were also analyzed between medication groups.

Results

182 patients were enrolled between June 2013 and July 2015: 50 on dabigatran, 123 on rivaroxaban, and 34 apixaban. INR values were mildly elevated among patients on dabigatran (median 1.3, IQR 1.1-1.4) and rivaroxaban (median 1.3, IQR 1.1-1.6) compared with apixaban (median 1.1, IQR 1.0-1.2). Patients on dabigatran had slightly higher than normal aPTT values (median 35, IQR 29.8-46.3), whereas those on rivaroxaban and apixaban did not. Fifty patients had TEG results. The median values for R, alpha, MA and lysis were normal for all groups. Prothrombin time (PT) and aPTT had a high correlation in all groups (dabigatran p=0.0005, rivaroxaban p<0.0001, and apixaban p<0.0001). aPTT correlated with the R value on TEG in patients on dabigatran (p=0.0094) and rivaroxaban (p=0.0028) but not apixaban (p=0.2532). Reversal occurred in 14%, 25%, and 18% of dabigatran, rivaroxaban, and apixaban patients, respectively. Both traditional measures of coagulopathy and TEG remained within normal limits after reversal.

Discussion

Neither traditional measures of coagulation nor TEG were able to detect coagulopathy in patients on NOAs.

Level of evidence

Level IV.

Non-Vitamin K Oral Anticoagulants Associated Bleeding and Its Antidotes

Oral anticoagulant-associated intracerebral hemorrhage (OAC-ICH) accounts for nearly 20% of all ICH. The number of patients with an indication for oral anticoagulant therapy (OAT) increases with increasing age. OAT became less complicate with the introduction of non-vitamin K oral anticoagulants (NOAC) OAT because of easier handling, favorable risk-benefit profile, reduced rates of ICH compared to vitamin K antagonists and no need for routine coagulation testing. Consequently, despite a better safety profile of NOAC the number of patients with OAC-ICH will increase. The mortality and complication rates of OAC-ICH are high and therefore they are the most feared complication of OAT. Immediate normalization of coagulation is the main goal and therefore knowledge of pharmacodynamics and coagulation status is essential. Laboratory measurements of anticoagulant activity in NOAC patients is challenging as specific tests are not widely available. More accessible tests such as the prothrombin time and activated partial thromboplastin time have important limitations. In dabigatran-associated ICH 5 g Idarucizumab should be administered. In rivaroxaban and apixaban-associated ICHs administration of andexanet alpha should be considered. Prothrombin complex concentrate may be considered if andexanet alpha is not available or in case of an ICH associated with edoxaban.

Point-of-care coagulation testing for reducing in-hospital delay in thrombolysis

Background:

The confirmation of prothrombin time international normalized ratio by a central laboratory often delays intravenous thrombolysis in patients with acute ischemic stroke.

Objectives:

We investigated the feasibility, reliability, and usefulness of point-of-care determination of prothrombin time international normalized ratio for stroke thrombolysis.

Methods:

Among 312 patients with ischemic stroke, 202 who arrived at the emergency room within 4.5 h of stroke onset were enrolled in the study. Patients with lost orders for point-of-care testing for the prothrombin time international normalized ratio or central laboratory testing for the prothrombin time international normalized ratio (n = 47) were excluded. We compared international normalized ratio values and the time interval from arrival to the report of test results (door-to-international normalized ratio time) between point-of-care testing for the prothrombin time international normalized ratio and central laboratory testing for the prothrombin time international normalized ratio. In patients who underwent thrombolysis, we compared the time interval from arrival to thrombolysis (door-to-needle time) between the current study population and historic cohort at our center.

Results:

In the 155 patients included in the study, the median door-to-international normalized ratio time was 9.0 min (interquartile range, 5.0–12.0 min) for point-of-care testing for the prothrombin time international normalized ratio and 46.0 min (interquartile range, 38.0–55.0 min) for central laboratory testing for the prothrombin time international normalized ratio (p < 0.001). The intraclass correlation coefficient between point-of-care testing for the prothrombin time international normalized ratio and central laboratory testing for the prothrombin time international normalized ratio was 0.975 (95% confidence interval: 0.966–0.982). Forty-nine of the 155 patients underwent intravenous thrombolysis. The door-to-needle time was significantly decreased after implementation of point-of-care testing for the prothrombin time international normalized ratio (median, 23.0 min; interquartile range, 16.0–29.8 vs median, 46.0 min; interquartile range, 33.5–50.5 min).

Conclusion:

Utilization of point-of-care testing for the prothrombin time international normalized ratio was feasible in the management of patients with acute ischemic stroke. Point-of-care testing for the prothrombin time international normalized ratio was quick and reliable and had a pivotal role in expediting thrombolysis.

Rivaroxaban plasma levels in acute ischemic stroke and intracerebral hemorrhage

OBJECTIVE

Information about rivaroxaban plasma level (RivLev) may guide treatment decisions in patients with acute ischemic stroke (AIS) and intracerebral hemorrhage (ICH) taking rivaroxaban.

METHODS

In a multicenter registry-based study (Novel Oral Anticoagulants in Stroke Patients collaboration; ClinicalTrials.gov: NCT02353585) of patients with stroke while taking rivaroxaban, we compared RivLev in patients with AIS and ICH. We determined how many AIS patients had RivLev ≤ 100ng/ml, indicating possible eligibility for thrombolysis, and how many ICH patients had RivLev ≥ 75ng/ml, making them possibly eligible for the use of specific reversal agents. We explored factors associated with RivLev (Spearman correlation, regression models) and studied the sensitivity and specificity of international normalized ratio (INR) thresholds to substitute RivLev using cross tables and receiver operating characteristic curves.

RESULTS

Among 241 patients (median age = 80 years, interquartile range [IQR] = 73-84; median time from onset to admission = 2 hours, IQR = 1-4.5 hours; median RivLev = 89ng/ml, IQR = 31-194), 190 had AIS and 51 had ICH. RivLev was similar in AIS patients (82ng/ml, IQR = 30-202) and ICH patients (102ng/ml, IQR = 51-165; p = 0.24). Trough RivLev_{(≤137ng/ml)} occurred in 126/190 (66.3%) AIS and 34/51 (66.7%) ICH patients. Among AIS patients, 108/190 (56.8%) had RivLev ≤ 100ng/ml. In ICH patients, 33/51 (64.7%) had RivLev ≥ 75ng/ml. RivLev was associated with rivaroxaban dosage, and inversely with renal function and time since last intake (each p < 0.05). INR ≤ 1.0 had a specificity of 98.9% and a sensitivity of 25.7% to predict RivLev ≤ 100ng/ml. INR ≥ 1.4 had a sensitivity of 59.3% and specificity of 90.1% to predict RivLev ≥ 75ng/ml.

INTERPRETATION

RivLev did not differ between patients with AIS and ICH. Half of the patients with AIS under rivaroxaban had a RivLev low enough to consider thrombolysis. In ICH patients, two-thirds had a RivLev high enough to meet the eligibility for the use of a specific reversal agent. INR thresholds perform poorly to inform treatment decisions in individual patients. Ann Neurol 2018;83:451-459.

Thrombolysis in stroke patients: Comparability of point-of-care versus central laboratory international normalized ratio

BACKGROUND

In acute stroke patients, thrombolysis is one gold standard therapy option within the first four hours after the ischemic event. A contraindication for thrombolysis is an International Normalized Ratio (INR) value >1.7. Since time is brain, rapid and reliable INR results are fundamental. Aim was to compare INR values determined by central laboratory (CL) analyzer and Point-of-Care Testing(POCT)-device and to evaluate the quality of POCT performance in cases of potential therapeutic thrombolysis at a certified stroke unit.

METHODS

In 153 patients INR measurements using POCT-devices (HEMOCHRON Signature Elite®) were compared to INR measurements (BCS®XP) performed at the central laboratory. Outlier evaluation was performed regarding the critical thrombolysis cut-off.

RESULTS

Overall, we demonstrated a significant correlation (r = 0.809, p<0.0001) between both measurement methods. Mean value of the absolute difference between CL-INR and POCT-INR measurements was 0.23. In 95.4% of these cases, no differences regarding the critical cut-off (INR 1.7) were observed. POCT-INR values tended to be higher than the CL-INR values (p = 0.01). In 4.6% cases, a different value regarding thrombolysis cut-off was found. All patients were >75 years.

CONCLUSIONS

POCT-INR measurements based on our POCT concept are suitable to determine INR values in critical stroke patients. Nevertheless, outlier evaluation is mandatory.

Management of acute stroke in patients on oral anticoagulants

PURPOSE OF REVIEW

An increasing number of patients are receiving oral anticoagulants. Since non-vitamin K antagonist oral anticoagulants (NOACs) were approved, primary prevention of ischemic stroke has become simpler. However, managing ischemic stroke and intracerebral hemorrhage while on oral anticoagulation (OAC) has become more complex. This review covers the latest developments in managing ischemic and hemorrhagic stroke in patients receiving vitamin K antagonists (VKA) and NOACs.

RECENT FINDINGS

Testing coagulation in patients with acute ischemic stroke and receiving NOACs is complex, and observational data challenge guideline recommendations. Initial registry and cohort data support the safety of endovascular therapy despite OAC. In intracerebral hemorrhage, rapid reversal of VKA can be achieved better with prothrombin complex concentrates than with fresh frozen plasma. Furthermore, rapid reversal seems to be associated with less hematoma expansion and better functional outcome. In addition, new evidence strongly supports resuming OAC after intracerebral hemorrhage. The unfavorable properties of NOAC-related intracerebral hemorrhage are similar to those associated with VKA.

SUMMARY

Translation of recent findings might improve both outcome in acute ischemic and hemorrhagic stroke in patients on oral anticoagulants and help refine clinical management. Data from randomized clinical trials are scarce.

A case report of parenchymal hematoma after intravenous thrombolysis in a rivaroxaban-treated patient: Is it a true rivaroxaban hemorrhagic complication?

RATIONALE

To date, the only treatment approved for acute ischemic strokes is thrombolysis. Whether intravenous thrombolysis may be safe in patients taking direct oral anticoagulants (DOACs) is currently a matter of debate.

PATIENT CONCERNS

A 74-year-old woman, who was on rivaroxaban 20 mg/d for nonvalvular atrial fibrillation, was admitted to our stroke unit with left-sided hemiparesis and aphasia. The onset of neurologic deficits had occurred 5 hours after the last rivaroxaban dose.

DIAGNOSIS

An acute ischemic stroke was diagnosed.

INTERVENTIONS

The patient was administered thrombolytic treatment with intravenous recombinant tissue plasminogen activator (r-TPA) 3 hours and 20 minutes after symptoms onset. Seven hours post-r-TPA treatment, the neurological deficit had worsened, and a type I intraparenchymal hematoma was detected on a computed tomography brain scan.

OUTCOMES

The clinical/neuroradiological picture improved significantly in the following days. The patient was discharged to a rehabilitation facility after 3 weeks.

LESSONS

In this case, factor ten activated (Xa) inhibitor, rivaroxaban might have increased the risk of hemorrhagic transformation of the ischemic stroke. However, this risk was overweighed by the benefit of thrombolysis, as the patient's clinical condition had improved significantly in the following weeks. The current guidelines discourage the use of thrombolytic treatment in patients with DOACs administered within the last 24(48) hours. However, the case reported herein and other world experiences, even though limited, suggest that an ongoing DOAC medication could no longer be considered a barrier to r-TPA treatment which may be a reasonable and valuable option, at least in selected acute stroke patients taking factor Xa inhibitors.

Intravenous Thrombolysis in Patients with Stroke Taking Rivaroxaban Using Drug Specific Plasma Levels: Experience with a Standard Operation Procedure in Clinical Practice

Background and Purpose

Standard operating procedures (SOP) incorporating plasma levels of rivaroxaban might be helpful in selecting patients with acute ischemic stroke taking rivaroxaban suitable for IVthrombolysis (IVT) or endovascular treatment (EVT).

Methods

This was a single-center explorative analysis using data from the Novel-Oral-Anticoagulants-in-Stroke-Patients-registry (clinicaltrials.gov:NCT02353585) including acute stroke patients taking rivaroxaban (September 2012 to November 2016). The SOP included recommendation, consideration, and avoidance of IVT if rivaroxaban plasma levels were <20 ng/mL, 20‒100 ng/mL, and >100 ng/mL, respectively, measured with a calibrated anti-factor Xa assay. Patients with intracranial artery occlusion were recommended IVT+EVT or EVT alone if plasma levels were ≤100 ng/mL or >100 ng/mL, respectively. We evaluated the frequency of IVT/EVT, door-to-needle-time (DNT), and symptomatic intracranial or major extracranial hemorrhage.

Results

Among 114 acute stroke patients taking rivaroxaban, 68 were otherwise eligible for IVT/EVT of whom 63 had plasma levels measured (median age 81 years, median baseline National Institutes of Health Stroke Scale 6). Median rivaroxaban plasma level was 96 ng/mL (inter quartile range [IQR] 18‒259 ng/mL) and time since last intake 11 hours (IQR 4.5‒18.5 hours). Twenty-two patients (35%) received IVT/EVT (IVT n=15, IVT+EVT n=3, EVT n=4) based on SOP. Median DNT was 37 (IQR 30‒60) minutes. None of the 31 patients with plasma levels >100 ng/mL received IVT. Among 14 patients with plasma levels ≤100 ng/mL, the main reason to withhold IVT was minor stroke (n=10). No symptomatic intracranial or major extracranial bleeding occurred after treatment.

Conclusions

Determination of rivaroxaban plasma levels enabled IVT or EVT in one-third of patients taking rivaroxaban who would otherwise be ineligible for acute treatment. The absence of major bleeding in our pilot series justifies future studies of this approach.

[Oral anticoagulant-associated intracerebral haemorrhage]

Intracerebral haemorrhage during treatment with oral anticoagulants is associated with high rates of morbidity and mortality. Impaired haemostasis can lead to progressive haematomas and, therefore, it should be identified early in order to initiate measures to reverse anticoagulation. Substitution of coagulation factors is essential in the treatment of these patients, but other intensive care measures such as blood pressure control are mandatory as well.

Point-of-care testing for emergency assessment of coagulation in patients treated with direct oral anticoagulants

Background

Point-of-care testing (POCT) of coagulation has been proven to be of great value in accelerating emergency treatment. Specific POCT for direct oral anticoagulants (DOAC) is not available, but the effects of DOAC on established POCT have been described. We aimed to determine the diagnostic accuracy of Hemochron® Signature coagulation POCT to qualitatively rule out relevant concentrations of apixaban, rivaroxaban, and dabigatran in real-life patients.

Methods

We enrolled 68 patients receiving apixaban, rivaroxaban, or dabigatran and obtained blood samples at six pre-specified time points. Coagulation testing was performed using prothrombin time/international normalized ratio (PT/INR), activated partial thromboplastin time (aPTT), and activated clotting time (ACT+ and ACT-low range) POCT cards. For comparison, laboratory-based assays of diluted thrombin time (Hemoclot) and anti-Xa activity were conducted. DOAC concentrations were determined by liquid chromatography-tandem mass spectrometry.

Results

Four hundred and three samples were collected. POCT results of PT/INR and ACT+ correlated with both rivaroxaban and dabigatran concentrations. Insufficient correlation was found for apixaban. Rivaroxaban concentrations at <30 and <100 ng/mL were detected with >95% specificity at PT/INR POCT ≤1.0 and ≤1.1 and ACT+ POCT ≤120 and ≤130 s. Dabigatran concentrations at <30 and <50 ng/mL were detected with >95% specificity at PT/INR POCT ≤1.1 and ≤1.2 and ACT+ POCT ≤100 s.

Conclusions

Hemochron® Signature POCT can be a fast and reliable alternative for guiding emergency treatment during rivaroxaban and dabigatran therapy. It allows the rapid identification of a relevant fraction of patients that can be treated immediately without the need to await the results of much slower laboratory-based coagulation tests.

Trial registration

Unique identifier, NCT02371070. Retrospectively registered on 18 February 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1619-z) contains supplementary material, which is available to authorized users.

Microfluidic coagulation assay for monitoring anticoagulant therapy in acute stroke patients

Reliable detection of anticoagulation status in patients treated with non-vitamin K antagonist oral anticoagulants (NOACs) is challenging but of importance especially in the emergency setting. This study evaluated the potential of a whole-blood clotting time assay based on Surface Acoustic Waves (SAW-CT) in stroke-patients. The SAW-technology was used for quick and homogenous recalcification of whole blood inducing a surface-activated clotting reaction quantified and visualised by real-time fluorescence microscopy with automatic imaging processing. In 20 stroke or transient ischaemic attack (TIA)-patients taking NOACs kinetics of SAW-CT were assessed and correlated to other coagulation parameters (PT, aPTT) and NOAC-plasma concentration measured by tandem mass spectrometry (LC-MS/MS). In 225 emergency patients with suspicion of acute stroke or TIA, SAW-CT values were assessed. Mean (± SD) SAW-CT in non-anticoagulated stroke patients (n=180) was 124 s (± 21). In patients on dabigatran or rivaroxaban, SAW-CT values were significantly higher 2 and 8 hours (h) after intake rising up to 267 seconds (s) (dabigatran, 2 h after intake) and 250 s (rivaroxaban, 8 h after intake). In patients on apixaban, SAW-CT values were only moderately increased 2 h after intake (SAW-CT 153 s). In emergency patients, SAW-CT values were significantly higher in NOAC and vitamin K antagonist (VKA)-treated as compared to non-anticoagulated patients. In conclusion, the SAW-CT assay is capable to monitor anticoagulant level and effect in patients receiving dabigatran, rivaroxaban and the VKA phenprocoumon. It has a limited sensitivity for apixaban-detection. If specific SAW-CT results were used as cut-offs, SAW-CT yields high diagnostic accuracy to exclude relevant rivaroxaban and dabigatran concentrations in stroke-patients.

Laboratory determination of old and new targeted anticoagulant agents for prevention of bleeding and thrombotic events in cancer patients

A two-fold prolongation of activated partial thromboplastin time (APTT) is established as therapeutic range for therapy with unfractionated heparin, hirudin and argatroban. The international normalized ratio (INR) of 2 to 3 is required to maintain anticoagulation in the therapeutic range of vitamin K antagonists. The therapeutic range of anti-factor Xa activity during therapy with low-molecular weight heparins and danaparoid are less well and of direct oral anticoagulants (DOAC) poorly defined. The relation of aPTT and INR values to thrombotic and bleeding events are well established despite a large variation of values in affected patients. The relation of coagulation values of the other anticoagulants to clinical events is open. The value of determination in cancer patients is higher because of the increased risk for thrombotic and bleeding events of this patient group. Several activities are currently undertaken to certify methods for in vitro diagnostic testing for DAOCs.

Coagulation Testing in Acute Ischemic Stroke Patients Taking Non–Vitamin K Antagonist Oral Anticoagulants

Background and Purpose—

In patients who present with acute ischemic stroke while on treatment with non–vitamin K antagonist oral anticoagulants (NOACs), coagulation testing is necessary to confirm the eligibility for thrombolytic therapy. We evaluated the current use of coagulation testing in routine clinical practice in patients who were on NOAC treatment at the time of acute ischemic stroke.

Methods—

Prospective multicenter observational RASUNOA registry (Registry of Acute Stroke Under New Oral Anticoagulants; February 2012–2015). Results of locally performed nonspecific (international normalized ratio, activated partial thromboplastin time, and thrombin time) and specific (antifactor Xa tests, hemoclot assay) coagulation tests were documented. The implications of test results for thrombolysis decision-making were explored.

Results—

In the 290 patients enrolled, nonspecific coagulation tests were performed in ≥95% and specific coagulation tests in 26.9% of patients. Normal values of activated partial thromboplastin time and international normalized ratio did not reliably rule out peak drug levels at the time of the diagnostic tests (false-negative rates 11%–44% [95% confidence interval 1%–69%]). Twelve percent of patients apparently failed to take the prescribed NOAC prior to the acute event. Only 5.7% (9/159) of patients in the 4.5-hour time window received thrombolysis, and NOAC treatment was documented as main reason for not administering thrombolysis in 52.7% (79/150) of patients.

Conclusions—

NOAC treatment currently poses a significant barrier to thrombolysis in ischemic stroke. Because nonspecific coagulation test results within normal range have a high false-negative rate for detection of relevant drug concentrations, rapid drug-specific tests for thrombolysis decision-making should be established.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01850797.

Novel oral anticoagulant management issues for the stroke clinician

BACKGROUND

Four nonvitamin K antagonist oral anticoagulants (NOACs) are approved for stroke prevention in patients with nonvalvular atrial fibrillation (NVAF).

AIMS

In this review, we assemble available evidence for the best management of ischemic and hemorrhagic stroke patients in the context of NOAC use.

SUMMARY OF REVIEW

NOACs provide predictable anticoagulation with fixed dosages. The direct thrombin inhibitor dabigatran and direct factor Xa inhibitors apixaban, edoxaban, and rivaroxaban are all noninferior to warfarin for the prevention of ischemic stroke and systemic embolism and are associated with reduced incidence of intracranial hemorrhage. While these agents offer treatment options for NVAF patients, they also present challenges specific to the clinician managing cerebrovascular disease patients.

CONCLUSIONS

We summarize available evidence and current approaches to the initiation, dosing, monitoring and potential reversal of NOACs in stroke patients.

Measuring non-vitamin K antagonist oral anticoagulant levels: When is it appropriate and which methods should be used?

Background

Although the need for an emergency intervention may merit laboratory measurement of non-vitamin K antagonist oral anticoagulant (NOAC) concentration or anticoagulant activity, NOACs are not supposed to require routine monitoring due to their stable pharmacological profiles compared with warfarin.

Aims

To examine situations where NOAC measurement may be useful and to provide information about methodologies available to measure NOAC-related anticoagulation activity.

Summary of review

The routine coagulation tests, including prothrombin time, thrombin time, activated partial thromboplastin time, and international normalized ratio, have variable sensitivities to NOACs. Tests have been developed for use with specific NOACs, e.g. diluted thrombin time or chromogenic factor Xa assays. In emergency situations, such as severe bleeding, stroke, or a requirement for urgent surgery or procedures, there may be a need to assess anticoagulant activity to guide clinical decision making. In cases where neutralization of the anticoagulant effect is warranted, specific reversal agents are likely to become invaluable medical tools. Evidence to date suggests that dosing decisions for NOACs based on clinical features (e.g. age or renal function) can help optimize the benefit–risk balance without assessment of anticoagulant activity in non-emergency routine situations.

Conclusions

Regular monitoring of NOAC levels does not provide benefits and cannot be recommended at present. In some specific circumstances, e.g. severe bleeding, before urgent surgery, or before thrombolysis, measurement may be beneficial to assess whether a patient is actively anticoagulated. The availability of NOAC-specific reversal agents may change management practices in emergencies.

A reliable aptamer array prepared by repeating inkjet-spotting toward on-site measurement

A preparation protocol is proposed for a reliable aptamer array utilizing an ink-jet spotter. We accumulated streptavidin and biotinylated-aptamer in this order on a biotinylated-polyethylene glycol-coated gold substrate to prepare an aptamer array. The aptamer array was prepared with an alternate spotting structure where each aptamer spot was placed between reference spots formed with blocking solution thus suppressing contamination from neighboring spots during the blocking and washing processes. Four aptamer spots were prepared in a small area of 1×4.8mm(2) with five reference spots made of blocking solution. We evaluated the thrombin binding ability of the spotted aptamer array using a multi-analysis surface plasmon resonance sensor. We prepared a disposable capillary-driven flow chip designed for on-site measurement (Miura et al., 2010) with our aptamer array and detected thrombin from phosphate-buffered saline at concentrations of 50ngmL(-1) and 1μgmL(-1) (equivalent to 1.35 and 27nM, respectively). A correlation was observed between the refractive index shift and thrombin concentration. This implies that our array preparation protocol meets the requirement for the preparation of a one-time-use chip for on-site measurement.

Non-Vitamin K Oral Anticoagulants in Stroke Patients: Practical Issues

Non-vitamin-K oral anticoagulants (NOACs) represent a major advance in the prevention of stroke in patients with atrial fibrillation (AF), offering a similar, if not superior, efficacy and safety profile and several practical advantages over oral vitamin K antagonists (VKAs). The rapid onset of action of the NOACs, their relatively short half-live, and the availability of specific reversal agents may be advantageous when managing acute ischemic strokes, and in the post-stroke, post-transient ischemic attack, and post-intracranial hemorrhage settings. In this review article, we offer practical guidance on the use of NOACs in these settings, focusing on managing the acute event and on initiating or resuming anticoagulation for secondary prevention. We also assess the use of NOACs to prevent stroke and bleeding in patients with AF who have chronic kidney disease, are elderly, or cognitively impaired, and we offer guidance on optimizing the use of NOACs and VKAs in these patient groups in the absence of evidence-based guidelines.