Are Screening Tests Reliable to Rule Out Direct Oral Anticoagulant Plasma Levels at Various Thresholds (30, 50, or 100 ng/mL) in Emergency Situations?

Hemostasis Testing in the Emergency Department: A Narrative Review

Routine laboratory screening is typically performed at initial evaluation of the vast majority of presentations to the emergency department (ED). These laboratory results are crucial to the diagnostic process, as they may influence up to 70% of clinical decisions. However, despite the usefulness of biological assessments, many tests performed are inappropriate or of doubtful clinical relevance. This overutilization rate of laboratory testing in hospitals, which represents a significant medical-economic burden, ranges from 20 to 67%, with coagulation tests at the top of the list. While reviews frequently focus on nonintensive care units, there are few published assessments of emergency-specific interventions or guidelines/guidance to date. The aim of this review is to highlight current recommendations for hemostasis evaluation in the emergency setting with a specific analysis of common situations leading to ED admissions, such as suspected venous thrombosis or severe bleeding. We revisit the evidence related to the assessment of patient's hemostatic capacity based on comprehensive history taking and physical examination as well as best practice recommendations for blood sample collection to ensure the reliability of results. This review also includes an examination of various currently available point of care tests and a comprehensive discussion on indications, limitations, and interpretation of these tests.

DOAC-Remove to counteract the interference of anti-Xa oral anticoagulants on the monitoring of heparin

INTRODUCTION

The monitoring of unfractionated heparin (UFH) by anti-factor Xa activity (AXA) is commonly used to ensure effective anticoagulation and prevent bleeding risk. However, in patients previously treated with an anti-Xa direct oral anticoagulant (DOAC) switching to UFH therapy, there is a risk of interference that may lead to inappropriate anticoagulation. The first objective of this study was to validate DOAC-Remove to remove DOAC for measuring UFH specific AXA. The second objective was to assess the length of DOAC interference on UFH monitoring and to identify potential predictive factors.

MATERIALS AND METHODS

This monocentric retrospective study included all patients admitted from April 2019 to April 2021 previously treated with anti-Xa DOAC, and for whom an interference on UFH monitoring was suspected. Interference was defined as a difference in the AXA measured before and after using DOAC-Remove >2.8-fold standard deviation of the method.

RESULTS

Removal with DOAC-Remove was specific of DOAC (apixaban n = 42, rivaroxaban n = 41, UFH n = 20) and sufficient to avoid interference on UFH AXA measurement. The exact interference length was 6.0 days [IQR 3.0-11.0] for apixaban (n = 26) and 4.5 days [IQR 2.0-5.8] for rivaroxaban (n = 20). Among the 89 patients sorted based on an interference length ≤ or >3 days, 74 (83.1%) presented an interference greater than 3 days. Correlations were observed with age for apixaban and creatinine for rivaroxaban.

CONCLUSIONS

Our results suggest that DOAC-Remove could be of high interest in patients receiving UFH previously treated with an anti-Xa DOAC even if DOAC was stopped for more than 3 days.

Is there a role for the laboratory monitoring in the management of specific antidotes of direct oral anticoagulants?

Given the growing number of patients receiving direct oral anticoagulant (DOAC), patients requiring rapid neutralization is also increasing in case of major bleedings or urgent surgery/procedures. Idarucizumab is commercialized as a specific antidote to dabigatran while andexanet alfa has gained the Food and Drug Administration and the European Medicines Agency approval as an oral anti-factor Xa inhibitors antidote. Other antidotes or hemostatic agents are still under preclinical or clinical development, the most advanced being ciraparantag. DOAC plasma levels measurement allows to appropriately select patient for antidote administration and may prevent unnecessary prescription of expensive molecules in some acute clinical settings. However, these tests might be inconclusive after some antidote administration, namely andexanet alfa and ciraparantag. The benefit of laboratory monitoring following DOAC reversal remains unclear. Here, we sought to provide an overview of the key studies evaluating the safety and efficacy of DOAC reversal using the most developed/commercialized specific antidotes, to discuss the potential role of the laboratory monitoring in the management of patients receiving DOAC specific antidotes and to highlight the areas that deserve further investigations in order to establish the exact role of laboratory monitoring in the appropriate management of DOAC specific antidotes.

Pearls and Pitfalls in the Measurement of Direct Oral Anticoagulants

Due to their widespread use, testing for direct oral anticoagulants (DOACs) has become urgent in certain clinical situations. Screening based on widely available, rapid, and simple hemostasis assays such as prothrombin time, activated partial thromboplastin time, or even diluted Russel Viper venom time may provide sufficient evidence of "over-coagulation" and could be used "in small/peripheral/spoke laboratories" as an emergency strategy, but is not thought to be reliable for driving clinical decision making. Given their good correlation with plasma concentration, urine dipsticks may be considered a valuable alternative for emergency screening, although their performance is dependent on renal function, may vary depending on the time since the last urination, and there may be problems of interfacing with the laboratory/hospital information system. Separation methods based on liquid chromatography and mass spectrometry may be clinically questionable, since they measure the concentration rather than the actual inhibitory effect of DOACs, are relatively expensive, cumbersome and time consuming, and therefore seem unsuitable for most conditions requiring urgent clinical decision making. A proposed approach therefore involves establishing a network of routine clinical laboratories, designating a reference center where DOAC tests could be available 24/7, establishing a clear diagnostic care pathway for ordering the tests from the laboratory and standard operating procedures for performing them, the use of the diluted thrombin time for dabigatran and anti-FXa assays (drug-calibrated) for rivaroxaban, apixaban, and edoxaban, as well as providing expert advice throughout the testing process, from ordering to interpretation of results.

Comparisons between diluted thrombin time, ecarin chromogenic assays, and UPLC-MS for plasma level dabigatran quantification: Results from DRIVING study

INTRODUCTION

The knowledge of dabigatran levels is helpful for decision-making in specific situations such as urgent surgery or when the question of reversal arises (uncontrolled bleeding, eligibility for thrombolysis). However, a limited number of observational studies are available regarding comparisons between quantification methods. The objective of the study was to compare dabigatran plasma levels using three assays including the reference method (high-performance liquid chromatography coupled with mass spectrometry), focusing on the agreement around the 30-50 ng/mL clinically relevant thresholds.

METHODS

Sixty healthy volunteers from DRIVING trial (NCT01627665) were given a single 300-mg dabigatran etexilate dose. Serial blood samplings were performed at pre-defined time points (0 to 24 h). We analyzed plasma samples using ultra-performance-liquid chromatography coupled with tandem mass spectrometry (UPLC-MS) (dabigatran reference method); ii/diluted thrombin time (dTT) (Hemoclot-DTI-Hyphen-Biomed); iii/ecarin-based chromogenic assay (ECA-II-Stago).

RESULTS

Nine hundred sixty samples were analyzed using the three assays (2759 values). dTT and ECA-II values were highly correlated with those of UPLC-MS (Deming regression). Most values >50 ng/mL were higher using dTT and ECA-II compared to UPLC-MS: biases were constant, +14% and +16% with dTT and ECA-II, respectively (Bland-Altman plots), suggesting that active metabolites accounted for ~15% of thrombin inhibition. Regarding values <30 ng/mL, 30-50 ng/mL, or ≥50 ng/mL, the agreement probability between dTT and ECA-II was of 90.6% [88.4-92.5] (Cohen's kappa coefficient 0.84).

CONCLUSION

dTT and ECA-II assays rapidly provide accurate dabigatran-level results for clinical practice, both assays being suitable in emergency, taking into account the thrombin inhibitory effect of dabigatran metabolites.

Usefullness of Heparin Calibrated Anti-Xa Activity to Assess Anticoagulant Activity of Apixaban and Rivaroxaban in Emergency Patients Scheduled for Acute Interventions

(1) Background: Direct oral anticoagulants (DOACs) require monitoring in some critical clinical situations. The specific tests for DOAC monitoring are not yet available in all labs. The aim of this study was to evaluate if a unique, more widespread heparin-calibrated anti-Xa assay could be suitable to estimate the concentrations of apixaban and rivaroxaban in order to establish an algorithm helping our clinicians in their therapeutic decision for patients treated with DOACs in emergencies. (2) Methods: A first retrospective part allowed us to determine of a conversion factor between the measured DOAC concentration and the deducted anti-Xa heparin activity based on optic density. During the second prospective part, both DOAC concentration (ng/mL) and anti-Xa activity heparin (UI/mL) were measured on the same sample, and the previously determined conversion factor was applied to each UI/mL value. We then compared the calculated and measured DOAC concentration values. (3) Results: The analysis of the derivation cohort confirmed a good correlation, especially between the anti-Xa heparin activity and the apixaban concentrations (r = 0.97). Additionally, we determined heparin-calibrated anti-Xa assay cut-offs for invasive procedures at 0.3 UI/mL and for intravenous thrombolysis at 0.51 UI/mL using ROC curves with a sensitivity at 98% and specificity at 95% for 0.3 UI/mL and a sensitivity at 97.7% and specificity at 88.2% for the cut-off of 0.51 UI/mL. In the validation cohort, we confirmed the agreement between measured and calculated DOAC concentrations for the low values, especially around cut-offs with an excellent negative predictive value for 0.51 UI/mL (94% for apixaban and 100% for rivaroxaban) and a good negative predictive value for 0.3 UI/mL (83.3% for apixaban and 85.7% for rivaroxaban). (4) Conclusions: Our results confirm that it is possible to correctly predict or exclude the presence of apixaban/rivaroxaban in emergency situations when specific tests are not readily available.

Comparison of Commercial Low Molecular Weight Heparin and Homemade Anti-Xa Calibrators to a Commercial Specific Anti-Xa Calibrator for Plasma Rivaroxaban Quantification by Anti-Xa Oral Anticoagulant Plasma Concentration Chromogenic Assay

Objective

The main concern about measuring the concentration of rivaroxaban by anti-Xa assay in some laboratories is the lack of a commercial specific calibrator in emergencies. Therefore, this study aimed at providing a homemade anti-Xa calibrator and commercial low molecular weight heparin (LMWH) anti-Xa calibrator.

Methods

The anti-Xa plasma concentration of rivaroxaban was measured in 70 patients using a commercial specific anti-Xa calibrator, a commercial LMWH anti-Xa calibrator, and a homemade anti-Xa calibrator.

Results

We demonstrated a significant correlation and agreement (P &lt; .001) between LMWH-calibrated anti-Xa and the commercial specific calibrator. A significant correlation (P &lt; .001) was found between homemade calibrated anti-Xa made by normal pooled plasma and that calibrated with a commercial specific drug. The nonspecific homemade and LMWH calibrators had excellent agreement (P &lt; .001) and can be used interchangeably.

Conclusion

Our data showed that for estimating rivaroxaban concentrations, the LMWH calibrator could be used as an alternative calibrator in the anti-Xa assay.

Heparin Anti-Xa Activity, a Readily Available Unique Test to Quantify Apixaban, Rivaroxaban, Fondaparinux, and Danaparoid Levels

BACKGROUND

Despite their usefulness in perioperative and acute care settings, factor-Xa inhibitor-specific assays are scarcely available, contrary to heparin anti-Xa assay. We assessed whether the heparin anti-Xa assay can (1) be used as a screening test to rule out apixaban, rivaroxaban, fondaparinux, and danaparoid levels that contraindicate invasive procedures according to current guidelines (>30 ng·mL-1, >30 ng·mL-1, >0.1 µg·mL-1, and >0.1 IU·mL-1, respectively), (2) quantify the anticoagulant level if found significant, that is, if it exceeded the abovementioned threshold.

METHODS

In the derivation cohort then in the validation cohort, via receiver operating characteristics (ROC) curve analysis, we evaluated the ability of heparin anti-Xa assay to detect levels of factor-Xa inhibitors above or below the abovementioned safety thresholds recommended for an invasive procedure (screening test). Among samples with relevant levels of factor-Xa inhibitor, we determined the conversion factor linking the measured level and heparin anti-Xa activity in a derivation cohort. In a validation cohort, the estimated level of each factor-Xa inhibitor was thus inferred from heparin anti-Xa activity. The agreement between measured and estimated levels of factor-Xa inhibitors was assessed.

RESULTS

Among 989 (355 patients) and 756 blood samples (420 patients) in the derivation and validation cohort, there was a strong linear relationship between heparin anti-Xa activities and factor-Xa inhibitors measured level (r = 0.99 [95% confidence interval {CI}, 0.99-0.99]). In the derivation cohort, heparin anti-Xa activity ≤0.2, ≤0.3, <0.1, <0.1 IU·mL-1 reliably ruled out a relevant level of apixaban, rivaroxaban, fondaparinux, and danaparoid, respectively (area under the ROC curve ≥0.99). In the validation cohort, these cutoffs yielded excellent classification accuracy (≥96%). If this screening test indicated relevant level of factor-Xa inhibitor, estimated and measured levels closely agreed (Lin's correlation coefficient close to its maximal value: 95% CI, 0.99-0.99). More than 96% of the estimated levels fell into the predefined range of acceptability (ie, 80%-120% of the measured level).

CONCLUSIONS

A unique simple test already widely used to assay heparin was also useful for quantifying these 4 other anticoagulants. Both clinical and economic impacts of these findings should be assessed in a specific study.

Coagulopathy in the surgical patient: trauma-induced and drug-induced coagulopathies

PURPOSE OF REVIEW

Coagulopathy is the derangement of hemostasis that in surgical patients may result in excessive bleeding, clotting or no measurable effect. The purpose of this review is to provide an overview of the most current evidence and practical approach to trauma- and drug-induced coagulopathy in surgical patients.

RECENT FINDINGS

Early identification and timely correction of coagulopathy in surgical patients with significant bleeding is paramount to prevent death and other consequences of hemorrhage. Trauma-induced coagulopathy is managed by protocols recommending fibrinogen replacement, FFP, platelets, TXA and frequent lab monitorization including viscoelastic tests. For warfarin- or DOAC-induced coagulopathy, the management follows similar principles plus drug reversal. Warfarin is diagnosed by prolonged international normalized ratio and reversed by PCC or FFP. DOACs are inconsistently diagnosed by routine coagulation tests, and reversed by a combination of TXA, PCC and specific antidotes (if available).

SUMMARY

Despite different understandings of the pathophysiology, trauma- and drug-induced coagulopathies are managed following similar protocols. In most of cases of significant surgical bleeding, timely and protocolized approach to correct the coagulopathy is likely to improve patients' outcome.

Rivaroxaban pharmacodynamics in healthy volunteers evaluated with thrombin generation and the active protein C system: Modeling and assessing interindividual variability

BACKGROUND

Rivaroxaban is a direct factor Xa inhibitor with substantial inter-individual pharmacokinetic (PK) variability. Pharmacodynamic (PD) variability, especially assessed with thrombin generation (TG), has been less documented.

OBJECTIVES

(i) To assess TG parameter time profiles in healthy volunteers, with TG being studied under different conditions and (ii) to model the relationship between rivaroxaban concentrations and TG parameters and subsequently estimate interindividual variability.

METHODS

Sixty healthy male volunteers (DRIVING-NCT01627665) received a single 40-mg rivaroxaban dose. Blood sampling was performed at baseline and 10 predefined time points over 24 h. The TG was investigated with the fully automated ST-Genesia system (Stago), using two tissue-factor (TF) concentrations, in the absence (-), or presence (+) of thrombomodulin (TM) for the lowest one. The PD models were built to characterize the relationships between plasma rivaroxaban concentrations and endogenous thrombin potential (ETP) or peak height induced by the lowest TF concentration.

RESULTS

Thrombin generation parameter time profiles with the lowest TF concentration showed a good sensitivity to rivaroxaban, especially +TM (active protein C negative feedback). The relationship between rivaroxaban concentrations and TG parameters was modeled with a sigmoidal relation. Mean rivaroxaban concentrations halving the baseline value of ETP and peak height (-TM) (C50 ) were of 284 and 33.2 ng/mL, respectively: +TM, C50 declined to 19.4 and 13.8 ng/mL, reflecting a powerful inhibitory effect. The estimated C50 population coefficients of variation were of 12.2% (-TM) and 31.3% (+TM) with the peak height models, 34.8% (+TM) with the ETP model.

CONCLUSIONS

This low-rivaroxaban to moderate-rivaroxaban PD variability in healthy volunteers contrasts with the substantial PK variability and deserves to be studied in different patient settings.

Anti-Xa Oral Anticoagulant Plasma Concentration Assay in Real Life: Rivaroxaban and Apixaban Quantification in Emergency With LMWH Calibrator

BACKGROUND

Oral anti-Xa inhibitors have demonstrated noninferiority to vitamin K antagonists (VKAs) for the prevention of stroke in patients with atrial fibrillation and recurrent venous thromboembolism. They are associated with a decrease in major bleeding. In contrast with VKA, no coagulation monitoring is required. However, in clinical practice, determination of drug concentration is sometimes necessary.

OBJECTIVE

The objective of this study was to evaluate a low-molecular-weight heparin (LMWH) calibrated anti-Xa assay for the quantification of rivaroxaban and apixaban plasma concentration in emergency.

METHODS

The anti-Xa plasma concentration of rivaroxaban and apixaban were measured in emergency in 210 patients using STA anti-Xa liquid assay. For each plasma concentration <150 ng/mL of rivaroxaban or apixaban, an anti-Xa assay calibrated with LMWH was performed.

RESULTS

We demonstrated a significant correlation between LMWH anti-Xa activity and rivaroxaban ( R² = 0.947) or apixaban ( R² = 0.959) concentration and a significant correlation between rivaroxaban and apixaban plasma concentration ( R² = 0.972). A LMWH anti-Xa activity <0.50 IU/mL could exclude a plasma concentration of rivaroxaban and apixaban >30 ng/mL and indicate the feasibility of invasive procedure. Conclusion and Relevance: In the absence of a specific test, LMWH-calibrated anti-Xa assay could be used to determine the presence and evaluate the plasma concentration of oral anti-Xa inhibitors. However, these initial findings require confirmation using other chromogenic calibrated oral anti-Xa assays.