Algorithm for Rapid Exclusion of Clinically Relevant Plasma Levels of Direct Oral Anticoagulants in Patients Using the DOAC Dipstick: An Expert Consensus Paper

BACKGROUND

 With the widespread use of direct oral anticoagulants (DOACs), there is an urgent need for a rapid assay to exclude clinically relevant plasma levels. Accurate and rapid determination of DOAC levels would guide medical decision-making to (1) determine the potential contribution of the DOAC to spontaneous or trauma-induced hemorrhage; (2) identify appropriate candidates for reversal, or (3) optimize the timing of urgent surgery or intervention.

METHODS AND RESULTS

 The DOAC Dipstick test uses a disposable strip to identify factor Xa- or thrombin inhibitors in a urine sample. Based on the results of a systematic literature search followed by an analysis of a simple pooling of five retrieved clinical studies, the test strip has a high sensitivity and an acceptably high negative predictive value when compared with levels measured with liquid chromatography tandem mass spectrometry or calibrated chromogenic assays to reliably exclude plasma DOAC concentrations ≥30 ng/mL.

CONCLUSION

 Based on these data, a simple algorithm is proposed to enhance medical decision-making in acute care indications useful primarily in hospitals not having readily available quantitative tests and 24/7. This algorithm not only determines DOAC exposure but also differentiates between factor Xa and thrombin inhibitors to better guide clinical management.

International Council for Standardization in Haematology Field Study Evaluating Optimal Interpretation Methods for Activated Partial Thromboplastin Time and Prothrombin Time Mixing Studies

CONTEXT.—

The prothrombin time (PT) and activated partial thromboplastin time (APTT) are screening tests used to detect congenital or acquired bleeding disorders. An unexpected PT and/or APTT prolongation is often evaluated using a mixing test with normal plasma. Failure to correct ("noncorrection") prolongation upon mixing is attributed to an inhibitor, whereas "correction" points to factor deficiency(ies).

OBJECTIVE.—

To define an optimal method for determining correction or noncorrection of plasma mixing tests through an international, multisite study that used multiple PT and APTT reagents and well-characterized plasma samples.

DESIGN.—

Each testing site was provided 22 abnormal and 25 normal donor plasma samples, and mixing studies were performed using local PT and APTT reagents. Mixing study results were evaluated using 11 different calculation methods to assess the optimal method based on the expected interpretation for factor deficiencies (correction) and noncorrection (inhibitor effect). Misprediction, which represents the failure of a mixing study interpretation method, was assessed.

RESULTS.—

Percentage correction was the most suitable calculation method for interpreting PT mixing test results for nearly all reagents evaluated. Incubated PT mixing tests should not be performed. For APTT mixing tests, percentage correction should be performed, and if the result indicates a factor deficiency, this should be confirmed with the subtraction III calculation where the normal pooled plasma result (run concurrently) is subtracted from the mixing test result with correction indicated by a result of 0 or less. In general, other calculation methods evaluated that performed well in the identification of factor deficiency tended to have high misprediction rates for inhibitors and vice versa.

CONCLUSIONS.—

No single method of mixing test result calculation was consistently successful in accurately distinguishing factor deficiencies from inhibitors, with between-reagent and between-site variability also identified.

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.

Activated Partial Thromboplastin Time and Prothrombin Time Mixing Studies: Current State of the Art

Mixing studies have long been in the clinical laboratory armamentarium for investigating unexpected, prolonged activated partial thromboplastin time (aPTT) or prothrombin time (PT). The purpose of the mixing study is to identify whether the aPTT/PT prolongation is secondary to a factor deficiency versus an inhibitor, which would present as a "corrected" and "noncorrected" mixing study, respectively. The differentiation between a factor deficiency and inhibitor may likely further direct clinical decisions, including additional diagnostic testing or factor replacement therapy. While aPTT/PT mixing studies are simple tests to perform, there is a lack of standardization for both the testing protocol and the interpretation of what is considered to be a corrected or noncorrected mixing study result. This review will describe the common indications for the mixing test, preanalytic variables that may affect mixing study performance, and describe several methods for interpreting the results of aPTT and PT mixing tests.

The Future of Laboratory-Developed Tests in Hemostasis Laboratories

Laboratory-developed tests (LDTs) are widely used in clinical hemostasis laboratories. The extent to which LDTs are regulated varies greatly around the world, and proposed changes to regulations have raised concerns about the future of LDTs in clinical laboratories. It is increasingly difficult to justify the use of an LDT where a commercially available method with regulatory approval is available. Conversely, where there is no suitable test with regulatory approval and there is a compelling clinical need, using an LDT outweighs the risk associated with not performing the test. We argue that LDTs are still required in specialist clinical laboratories to fulfill unmet clinical needs, and in lower middle-income countries where they are a vital resource.

Factor VIII and Factor IX Activity Measurements for Hemophilia Diagnosis and Related Treatments

Accurate measurement of clotting factors VIII (FVIII) or IX (FIX) is vital for comprehensive diagnosis and management of patients with hemophilia A or B. The one-stage activated partial thromboplastin time (aPTT)-based clotting assay is the most commonly used method worldwide for testing FVIII or FIX activities. Alternatively, FVIII and FIX chromogenic substrate assays, which assess the activation of factor X, are available in some specialized laboratories. The choice of reagent or methodology can strongly influence the resulting activity. Variation between one-stage FVIII or FIX activities has been reported in the measurement of some standard and extended half-life factor replacement therapies and gene therapy for hemophilia B using different aPTT reagents. Discrepancy between one-stage and chromogenic reagents has been demonstrated in some patients with mild hemophilia A or B, the measurement of some standard and extended half-life factor replacement therapies, and the transgene expression of hemophilia A and B patients who have received gene therapy. Finally, the measurement of bispecific antibody therapy in patients with hemophilia A has highlighted differences between chromogenic assays. It is imperative that hemostasis laboratories evaluate how suitable their routine assays are for the accurate measurement of the various hemophilia treatment therapies.

From Ink Pens to Computers: A Personal Look Back at Landmark Changes during 5 Decades as a Clinical Laboratory Scientist in U.S. Hemostasis Laboratories

In 2023, Seminars in Thrombosis and Hemostasis will be celebrating its 50^th anniversary, and similarly this will also mark my 5^th decade of working in, or association with, laboratories that perform hemostasis testing. My career started at a large military medical center, but I also worked at several other facilities, including military dispensaries, community hospitals, and a large academic institution. The difference between each type of hemostasis laboratory was as expected, with larger facilities having better instrumentation and more prolific test menus. However, whether one worked in a large academic center, or a small rural hospital, regulatory changes affected every clinical laboratory to the same degree. Advances in technology also eventually affected every hemostasis laboratory, but these salient changes were more likely to occur earlier at the larger institutions. As Seminars in Thrombosis and Hemostasis celebrates its 50^th anniversary, that milestone triggered recollection about those salient events that occurred during my own career in hemostasis testing. As such, I describe (my impression) the top ten landmark changes that altered laboratory practice at the facilities where I worked during the past 5 decades.

Ecarin-Based Methods for Measuring Thrombin Inhibitors

Ecarin is a venom from the saw-scaled viper, Echis carinatus, which catalyzes prothrombin into meizothrombin. This venom is used in several hemostasis laboratory assays, including ecarin clotting time (ECT) and ecarin chromogenic assays (ECA). The use of these ecarin-based assays was first implemented as a tool for monitoring the infusion of a direct thrombin inhibitor, hirudin. Subsequently, this method has been more recently employed for measuring either the pharmacodynamic or pharmacokinetic properties of the oral direct thrombin inhibitor, dabigatran. In this chapter, the procedure for performing manual ECT and automated and manual ECA for measuring thrombin inhibitors is described.

An Acute Need Inspiration: Autoneutralization of Lupus Anticoagulants in Affected Prothrombin Times (PT) and Activated Partial Thromboplastin Times (APTT)

Lupus anticoagulants are antibodies directed to phospholipids (PL) and in particular represent an in vitro phenomenon where these antibodies bind to PL in coagulation reagents creating an artificial prolongation of the activated partial thromboplastin time (APTT) and sometimes also prothrombin time (PT) clotting times. Prolongation of LA-induced clotting times is typically not associated with bleeding risk. However, the degree of prolongation may cause some trepidation for clinicians that will be performing delicate surgeries or those with high bleeding risks, so a mechanism to alleviate their anxiety may be prudent. As such, an autoneutralizing method to mitigate or eliminate the LA effect on the PT and APTT may be beneficial. In this document, the detailing of an autoneutralizing procedure to diminish the LA effect on the PT and APTT will be provided.

Preparing Surrogate Abnormal Quality Control Samples for Platelet Function Studies and Viscoelastic Testing

In the United States, published options for clinical laboratories to perform quality control (QC) procedures less stringent than the regulatory requirements (Clinical and Laboratory Improvement Act, CLIA) based on risk assessment, although the laboratory must perform to manufacturer's minimum requirements. The US requirements for internal quality control requires at least two levels of control material every 24 h of patient testing. For some coagulation testing, the recommended quality control may be a normal sample or commercial controls that do not address all reporting components of the test. Additional circumstances and difficulties in achieving this minimum QC requirement can be due to either (1) nature of the sample type (i.e., whole blood sample requirements), (2) lack of commercial or suitable control material, or (3) unusual or rare samples. The purpose of this chapter is to provide provisional guidance for laboratory sites to prepared samples to verify the performance of reagents and testing performance of platelet function studies and viscoelastic measurements.

Hemostasis and Thrombosis: An Overview Focusing on Associated Laboratory Testing to Diagnose and Help Manage Related Disorders

Hemostasis is a complex but balanced process that permit normal blood flow, without adverse events. Disruption of the balance may lead to bleeding or thrombotic events, and clinical interventions may be required. Hemostasis laboratories typically offer an array of tests, including routine coagulation and specialized hemostasis assays used to guide clinicians for diagnosing and managing patients. Routine assays may be used to screen patients for hemostasis-related disturbances but may also be used for drug monitoring, measuring efficacy of replacement or adjunctive therapy, and other indications, which may then be used to guide further patient management. Similarly, "specialized" assays are used for diagnostic purposes or may be used to monitor or measure efficacy of a given therapy. This chapter provides an overview of hemostasis and thrombosis, with a focus on laboratory testing that may be used to diagnose and help manage patients suspected of hemostasis- and thrombosis-related disorders.

Preanalytical Variables in Hemostasis Testing

Hemostasis testing performed in clinical laboratories are critical for assessing hemorrhagic and thrombotic disorders. The assays performed can be used to provide the information required for diagnosis, risk assessment, efficacy of therapy, and therapeutic monitoring. As such, hemostasis tests should be performed to the highest level of quality, including the standardization, implementation, and monitoring of all phases of the testing, which include the preanalytical, analytical, and post-analytical phases. It is well established that the preanalytical phase is the most critical component of the testing process, being the hands-on activities, including patient preparation for blood collection, as well as the actual blood collection, including sample identification and the post-collection handling to include sample transportation, processing, and storage of samples when testing is not performed immediately. The purpose of this article is to provide an update to the previous edition of coagulation testing-related preanalytical variables (PAV) and, when properly addressed and performed, can reduce the most common causes of errors in the hemostasis laboratory.

Post-analytical Issues in Hemostasis and Thrombosis Testing: An Update

There are typically three phases identified as contributing to the total testing process. The preanalytical phase starts with the clinician and the patient, when laboratory testing is being considered. This phase also includes decisions about which tests to order (or not), patient identification, blood collection, blood transport, sample processing, and storage to name a few. There are many potential failures that may occur in this preanalytical phase, and these are the topic of another chapter in this book. The second phase, the analytical phase, represents the performance of the test, which is essentially covered in various protocols in this book and the previous edition. The third is the post-analytical phase, which is what occurs after sample testing, and is the topic of the current chapter. Post-analytical issues are generally related to reporting and interpretation of test results. This chapter provides a brief description of these events, as well as guidance for preventing or minimizing post-analytical issues. In particular, there are several strategies for improved post-analytical reporting of hemostasis assays, with this providing the final opportunity to prevent serious clinical errors in patient diagnosis or management.

Protocols for D-Dimer Measurements for Aid to Diagnosis or Exclusion of Venous Thromboembolism

Measuring D-dimer is commonly used as a surrogate to indicate a clot-forming process, with subsequent lysis. This test has two primary intended uses: (1) as aid to diagnosis of various conditions and (2) venous thromboembolism (VTE) exclusion. If the manufacturer cites a VTE exclusion claim, the D-dimer test must only be used in evaluating patients with a non-high or unlikely pretest probability for pulmonary embolism and deep vein thrombosis. D-dimer kits with only aid to diagnosis claim should not be used for VTE exclusion. The intended use of the D-dimer may vary by region, and readership should consult manufacturer instructions for use to assure proper use of the assay. In this chapter, several methods for measuring D-dimer will be described.

Ultracentrifugation for Coagulation Testing

Lipemia is known to potentially affect coagulation testing. It may be detected with newer coagulation analyzers that are validated to assess hemolysis, icterus, and lipemia (HIL) in a plasma sample. In samples with lipemia where accuracy of the test result is compromised, strategies for mitigating the lipemia interferences would be required. The tests affected by lipemia are those using chronometric, chromogenic, immunologic, or other light scattering/reading principles. Ultracentrifugation is one process that has been effectively demonstrated to remove lipemia from blood samples to allow for more accurate measurements. In this chapter, a description of one ultracentrifugation method is provided.

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.

Guidance on the critical shortage of sodium citrate coagulation tubes for hemostasis testing

Recent manufacturing problems and increased utilization has created a shortage of 3.2% sodium citrate blood collection tubes used for coagulation testing, causing stakeholders such as hospitals, clinics and laboratories, to find suitable alternatives. Considerations for in-house citrate blood collection tube preparations or purchasing commercial products from unknown manufacturing sources is of particular concern to laboratories that perform coagulation testing. It is well recognized that variability exists between citrate blood collection tube manufacturers, thereby making any transition to new blood collection methods more challenging than simply switching to a new source. This document provides provisional guidance for validating alternative sources of sodium citrate blood collection tubes (commercial or in-house preparations) prior to clinical implementation.

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).

Impact of water temperature on reconstitution of quality controls for routine hemostasis testing

BACKGROUND

This study aimed to investigate whether the temperature of distilled water used for reconstituting lyophilized routine internal quality control (IQC) material may influence the process of validation of analytical sessions of routine hemostasis testing.

METHODS

Routine hemostasis testing was performed for 10 consecutive days using two levels of IQC materials dissolved using distilled water at three different temperatures (2-4°C, 22-24°C and 36-38°C). The tests assayed comprised prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (FBG), antithrombin (AT), protein C (PC), protein S (PS) and D-dimer (D-Dimer HS 500), using the same ACL TOP 700 hemostasis instrument.

RESULTS

Overall, 50% (i.e. 7/14) IQC measurements displayed statistically significant bias when lyophilized material was dissolved with distilled water at 3-5°C compared to 22-24°C, and in two instances (level I for both PT and D-dimer) the bias was higher than the quality specifications. Concerning lyophilized material dissolved with distilled water at 36-38°C, 21% (3/14) IQC values displayed a statistically significant bias compared to 22-24°C, and in one instance (level 2 for PT) the bias was higher than the quality specifications.

CONCLUSIONS

The results of this study show that water temperature, as used to dissolve lyophilized IQC material, may represent an important pre-analytical variable in routine hemostasis testing, especially cold temperatures. Laboratory professionals are encouraged to standardize water temperature, preferably between 22 and 24°C, before reconstituting lyophilized IQC materials used to validate routine hemostasis testing.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the verification of haemostasis analyser-reagent test systems. Part 2: Specialist tests and calibrated assays

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance, verification and implementation processes required by regulatory and accreditation bodies. It covers the planning and verification of specialist haemostatic tests, including factor assays, D-dimers, direct anticoagulants and thrombophilia testing.

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.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the evaluation of haemostasis analyser-reagent test systems. Part 1: Instrument-specific issues and commonly used coagulation screening tests

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance of verification, validation and implementation processes required by regulatory and accreditation bodies. It covers the planning and execution of an evaluation of the commonly performed screening tests (prothrombin time, activated partial thromboplastin time, thrombin time and fibrinogen assay), and instrument-specific issues. Advice on selecting an appropriate haemostasis analyser, planning the evaluation, and assessing the reference, interval, precision, accuracy, and comparability of a haemostasis test system are also given. A second companion document will cover specialist haemostasis testing.

Ecarin based coagulation testing

Ecarin is derived from venom of Echis carinatus, and will activate prothrombin into meizothrombin which will then cleave fibrinogen to result in clot formation. Ecarin based testing has been described for decades, but these assays were typically restricted to reference or speciality coagulation laboratories. This test was initially described for the assessment of direct thrombin inhibitors (eg, bivalirudin lepirudin, or argatroban) and was not affected by heparins or heparinoids. Ecarin based assays were rarely used for anticoagulation monitoring until the emergence of the direct oral thrombin inhibitor dabigatran etexilate in 2010. As this test was mentioned in the prescribing information for dabigatran etexilate, there was increased interest for use by clinical laboratories as the preferred method for assessing the anticoagulant effect of this drug. The purpose of this document is to review the current status of ecarin based assays for assessing dabigatran. This is with the understanding that these methods can also be exploited for determining the anticoagulation effect of parenteral direct thrombin inhibitors, such as argatroban and bivalirudin.

International Council for Standardization in Haematology Recommendations for Hemostasis Critical Values, Tests, and Reporting

This guidance document was prepared on behalf of the International Council for Standardization in Haematology (ICSH), the aim of which is to provide hemostasis-related guidance documents for clinical laboratories. The current ICSH document was developed by an ad hoc committee, comprising an international collection of both clinical and laboratory experts. The purpose of this ICSH document is to provide laboratory guidance for (1) identifying hemostasis (coagulation) tests that have potential patient risk based on analysis, test result, and patient presentations, (2) critical result thresholds, (3) acceptable reporting and documenting mechanisms, and (4) developing laboratory policies. The basis for these recommendations was derived from published data, expert opinion, and good laboratory practice. The committee realizes that regional and local regulations, institutional stakeholders (e.g., physicians, laboratory personnel, hospital managers), and patient types (e.g., adults, pediatric, surgical) will be additional confounders for a given laboratory in generating a critical test list, critical value thresholds, and policy. Nevertheless, we expect this guidance document will be helpful as a framework for local practice.

Preanalytical Variables in Coagulation Testing: Setting the Stage for Accurate Results

Many preanalytical variables may affect the results of routine coagulation assays. While advances in laboratory instrumentation have partially addressed the laboratory's ability to recognize some of these variables, there remains an increased reliance on laboratory personnel to recognize the three potential areas where coagulation testing preanalytical issues may arise: (1) specimen collection (including patient selection), (2) specimen transportation and stability, and (3) specimen processing and storage. The purpose of this article is to identify the preanalytical variables associated with coagulation-related testing and provide laboratory practice recommendations in an effort to improve the quality of coagulation testing and accuracy of result reporting.

An update on laboratory assessment for direct oral anticoagulants (DOACs)

The first direct oral anticoagulant (DOAC) to be approved for clinical use was dabigatran, a direct thrombin inhibitor, in 2010. Since that time, four additional DOACs, all direct anti-Xa inhibitors, have been approved, including rivaroxaban, apixaban, edoxaban and betrixaban. Our knowledge about the effect of DOACs on laboratory testing, as well as the use of the laboratory for measuring DOACs has been an evolving process. These drugs are not routinely monitored in the same fashion as coumadin, but there is an increasing demand on the laboratory to have the capacity to adequately assess DOAC anticoagulant effect (pharmacodynamics) or levels (pharmacokinetics) in either emergent or the routine situations. This manuscript provides an update on laboratory guidance and progress of methods for measuring DOACs.

International Council for Standardization in Haematology (ICSH) Recommendations for Laboratory Measurement of Direct Oral Anticoagulants

This guidance document was prepared on behalf of the International Council for Standardization in Haematology (ICSH) for providing haemostasis-related guidance documents for clinical laboratories. This inaugural coagulation ICSH document was developed by an ad hoc committee, comprised of international clinical and laboratory direct acting oral anticoagulant (DOAC) experts. The committee developed consensus recommendations for laboratory measurement of DOACs (dabigatran, rivaroxaban, apixaban and edoxaban), which would be germane for laboratories assessing DOAC anticoagulation. This guidance document addresses all phases of laboratory DOAC measurements, including pre-analytical (e.g. preferred time sample collection, preferred sample type, sample stability), analytical (gold standard method, screening and quantifying methods) and post analytical (e.g. reporting units, quality assurance). The committee addressed the use and limitations of screening tests such as prothrombin time, activated partial thromboplastin time as well as viscoelastic measurements of clotting blood and point of care methods. Additionally, the committee provided recommendations for the proper validation or verification of performance of laboratory assays prior to implementation for clinical use, and external quality assurance to provide continuous assessment of testing and reporting method.

Clinical pearls: Laboratory assessments of direct oral anticoagulants (DOACS)

Direct oral anticoagulants (DOACS) are being used for stroke prevention in patients with atrial fibrillation as well as for prophylaxis and treatment of venous thromboembolism. Clinicians who treat, or may encounter, patients with DOAC exposure, should be aware of the limitations of coagulation testing in this setting, and seek counsel from their laboratory to understand the effects of DOACS on coagulation results. Generally, assays that employ clot based principles, or methods that require thrombin or Factor Xa activation or substrates may be affected by the presence of DOACS. The clinical laboratory should have an algorithmic testing plan for adequately assessing the presence of all DOACS and readily provide this information to clinicians. We describe Clinical Pearls for DOAC assessment using common and esoteric coagulation testing.

The danger of relying on the APTT and PT in patients on DOAC therapy, a potential patient safety issue

Prolongation of the activated partial thromboplastin time (APTT) and prothrombin time/international normalized ratio (PT/INR) correlates poorly with plasma concentrations of direct oral anticoagulant agents (DOACS) including direct thrombin and direct Xa inhibitors. It has been repeatedly demonstrated that patients can have normal APTT and PT/INR with a therapeutic plasma concentration of a DOAC. Clinicians can no longer rely on a normal APTT and PT to determine that an anticoagulated patient is safe to undergo an invasive procedure. Laboratory scientists need to play a key and active role in educating clinicians about the limitations of the APTT and PT in patients on DOAC prophylaxis or therapy.

Laboratory Assessment of Direct Oral Anticoagulants

Oral vitamin K anticoagulation (warfarin, Coumadin, coumarin) has long been used for long-term treatment and prophylaxis in a variety of clinical settings. Given the unpredictable pharmacokinetic and food impact of warfarin, episodic monitoring is required. Since the early 2000s, direct oral anticoagulants (DOACs) entered into clinical trials as a potential alternative strategy to oral vitamin K antagonists for long-term anticoagulation. As these drugs have predictable pharmacokinetics and pharmacodynamics, there was no requirement for episodic or routine monitoring. However, shortly after their introduction into clinical use, it became apparent that certain emergent or acute situations may require some capacity to measure these drugs, especially in a bleeding patient with DOAC exposure. The scramble for literature and data to support or suggest laboratory methods which can rapidly and accurately quantify or estimate DOAC concentration soon began. This review describes the literature to date, and recommendations for laboratories to provide tests that will assure either the presence/absence of DOAC or the capacity to quantify DOAC using rapid methods that could be implemented on most clinical laboratory instruments.

Measuring Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs) can be quantified using methods that can be performed in any clinical or research laboratory using manual or automated instrument platforms. Dabigatran etexilate, the oral direct thrombin inhibitor, can be quantified by drug-calibrated clot or chromogenic-based assays using either thrombin or ecarin as substrates. Oral direct anti-Xa inhibitors, such as rivaroxaban, apixaban, and edoxaban, can be quantified with drug-calibrated anti-Xa kits or reagents as typically used for measuring heparins (unfractionated, low molecular weight, or pentasaccharides).

The laboratory's 2015 perspective on direct oral anticoagulant testing

The introduction of direct oral anticoagulant (DOAC) therapy into clinical use in the past 5 years has had significant impact on the clinical laboratory. Clinicians' desire to determine plasma drug presence or measure drug concentration, and more recent observations regarding the limitations and utility of coagulation testing in the setting of DOAC treatment, suggest that early published recommendations regarding laboratory testing should be reassessed. These initial recommendations, furthermore, were often based on drug-spiked plasma studies, rather than samples from patients receiving DOAC therapy. We have demonstrated that reagent sensitivity varies significantly whether drug-spiked samples or samples from DOAC-treated patients are tested. Data from drug-enriched samples must therefore be interpreted with caution or be used as a guide only. We present laboratory assays that can be used to determine drug presence and to measure drug concentration, and provide recommended testing algorithms. As DOAC therapy may significantly impact on specialty coagulation assays, we review those tests with the potential to give false-positive and false-negative results.

A single test to assay warfarin, dabigatran, rivaroxaban, apixaban, unfractionated heparin, and enoxaparin in plasma

Essentials Simple and fast assaying of different anticoagulants (ACs) is useful in emergent situations. We used highly diluted prothrombin time (dPT) or highly diluted Fiix-PT (dFiix-PT) to assay ACs. Both tests could quantify target specific anticoagulants and warfarin anticoagulation. Improved results were consistently observed with the dFiix-PT compared with the dPT.

SUMMARY

Background Assaying anticoagulants is useful in emergency situations or before surgery. Different specific assays are currently needed depending on the anticoagulant. Objectives We hypothesized that levels of warfarin, dabigatran, rivaroxaban, apixaban, and heparins could be measured with use of the diluted prothrombin time (dPT) and diluted Fiix-PT (dFiix-PT), using highly diluted thromboplastin (TP). The latter test is affected only by reduced levels of active factors II and X but corrects test plasma for other deficiencies Methods Increasing TP dilutions were used to identify suitable dilutions to measure dabigatran, rivaroxaban, apixaban, unfractionated heparin (UFH), and enoxaparin. Calibrators containing known amounts of direct oral anticoagulants (DOACs) were used to make standard curves. Citrated plasma samples were obtained from patients taking warfarin or DOACs with known drug concentrations as determined by specific assays. Results The dFiix-PT at a TP dilution of 1:1156 could be used to measure all of the drugs tested at therapeutic concentrations except for fondaparinux. The dPT achieved the same but required two TP dilutions (1:750 and 1:300). The warfarin effect could be assessed by using dFiix-PT at 1:1156 with a PT ratio identical to the international normalized ratio. Six different TPs yielded similar results, but two were less sensitive. Dabigatran, rivaroxaban, and apixaban could be accurately measured in patient samples using both dilute PT assays, but a better correlation was consistently observed between the dFiix-PT and specific assays than with the dPT. Conclusion The dFiix-PT using a single dilution of TP may be suitable to assess the anticoagulant effects of warfarin, dabigatran, rivaroxaban, apixaban, heparin, and enoxaparin.

Assessing nonvitamin K antagonist oral anticoagulants (NOACs) in the laboratory

Nonvitamin K antagonist oral anticoagulants (NOACs) are being used with increasing frequency due to their safety profile, ease of use, and given that therapeutic monitoring is not required. As these agents have only recently been FDA approved, their effect on routine and specialty coagulation assays is not well appreciated. This article discusses NOAC effect on routine coagulation assays and whether these assays can be used to estimate drug concentration as well as which assays are suitable to quantitate drug concentration in plasma. Also reviewed is the use of manufactured drug calibrators to determine reagent responsiveness and the effect of these agents on various special coagulation assays.

Verifying the performance characteristics of the TEG5000 thromboelastogram in the clinical laboratory

OBJECTIVE

To verify the manufacturer performance claims of the TEG5000 with traditional laboratory methods.

MATERIALS AND METHODS

Samples were concurrently measured using the TEG5000 analyzer and either PT, APTT, fibrinogen, factor activities, platelet count, or platelet function testing using whole blood or platelet-rich plasma methods.

RESULTS

Within-run imprecision yielded coefficient of variation (CV) of <5%. There was no correlation of PT or APTT with R time. Only Factor VIII and factor XII activity significantly correlated with R time. There was significant correlation between k and angle with FBG, PLT count, and factor levels. There was weak inverse correlation between angle results and measures of platelet function. All laboratory methods were significantly correlated with MA. There were significant differences between citrated whole blood and fresh citrated plasma for angle and MA, and between fresh and frozen plasma for R time and MA. We demonstrated a high % inhibition noted with normal, drug naïve donors, especially with ADP PLT mapping (50% inhibition), but less so with AA PLT mapping (20% inhibition). For TEG platelet mapping, 19/22 (86.3%) and 17/22 (77.3%) results were concordant with traditional aggregation results.

CONCLUSION

We demonstrated both the lack of, and strong correlation between laboratory tests and the TEG parameters.

Heparin-Calibrated Chromogenic Anti-Xa Activity Measurements in Patients Receiving Rivaroxaban

Background: Determination of plasma rivaroxaban concentration may be necessary in certain clinical situations. Rivaroxaban concentration can be accurately and rapidly determined using a chromogenic anti–activated factor X (factor Xa) assay with specific drug calibrator material. However, there are currently no Food and Drug Administration (FDA)-approved rivaroxaban calibrators available in the United States. Objective: To determine whether FDA-approved commercial kits for measuring heparin anti–factor Xa activity can be used to assess rivaroxaban concentrations when calibrated for unfractionated heparin or low-molecular-weight heparins. Methods: Trough and peak samples were taken from 30 patients taking rivaroxaban as part of their routine care for atrial fibrillation or venous thromboembolism. The samples were tested using 3 different FDA-approved commercial kits for measuring heparin anti–factor Xa activity. Results: There was acceptable correlation between rivaroxaban levels and heparin anti–factor Xa activity using Berichrom and COAMATIC heparin kits. The STA liquid heparin method was the most sensitive to presence of rivaroxaban. Conclusion: This study demonstrates a strong correlation, but variability between kits, for assessing rivaroxaban concentrations using heparin anti–factor Xa assays. The extent of the heparin calibration curve significantly limits the measurable rivaroxaban range, and this application may be useful only for trough samples. The STA liquid heparin, being exquisitely sensitive to rivaroxaban, may be suitable for ruling out presence of the drug. The routine use of heparin-calibrated anti–factor Xa assays to quantify rivaroxaban is not advocated, and when applied, it must be used with caution and limitations clearly understood.

Comparison of Anti-Xa and Dilute Russell Viper Venom Time Assays in Quantifying Drug Levels in Patients on Therapeutic Doses of Rivaroxaban

Context

Rivaroxaban is a new oral anticoagulant that functions as a direct anti-Xa inhibitor. Although routine monitoring is not required, measurement of plasma concentrations may be necessary in certain clinical situations. Routine coagulation assays, such as the prothrombin time and, to a lesser degree, activated partial thromboplastin time, correlate with drug concentration, but because of reagent variability, these methods are not reliable for determining rivaroxaban anticoagulation.

Objective

To compare different methods and calibrators for measuring rivaroxaban, including the chromogenic anti-Xa assay, which, when calibrated with a rivaroxaban standard, may be more appropriate for determining anticoagulation.

Design

We compared measured rivaroxaban concentrations with the same anti-Xa kit but used different calibrators, with different anti-Xa kits but the same calibrators, with antithrombin-supplemented anti-Xa kit versus nonsupplemented kits, and with 2 methods based on rivaroxaban-calibrated, high-phospholipid, dilute Russell viper venom time. Regression and paired t test statistics were used to determine correlation and significant differences among methods and calibrator sources.

Results

Although there was strong correlation, statistically significant biases existed among methods that report rivaroxaban levels. A single-source calibrator did not alleviate those differences among methods. High-phospholipid Russell viper venom reagents correlated with rivaroxaban concentration but were not better than chromogenic anti-Xa methods.

Conclusions

Rivaroxaban-calibrated, anti-Xa measurements correlate well, but the clinical significance of the variation with rivaroxaban measurements is uncertain. The antithrombin-supplemented, anti-Xa method should be avoided for measuring rivaroxaban.

Evaluating the use of commercial drug-specific calibrators for determining PT and APTT reagent sensitivity to dabigatran and rivaroxaban

Suitable laboratory methodologies for quantifying the non-vitamin K oral anticoagulants (NOAC) include liquid chromatography-tandem mass spectrometry (LC-MS/MS) or drug-calibrated assays such as the dilute thrombin time for dabigatran or anti-Xa measurements for rivaroxaban. In situations when these tests are unavailable, it has been suggested that using commercial drug calibrators on APTT and PT assays would theoretically provide reagent sensitivity to these drugs. The purpose of this study was to determine whether commercial drug calibrators deliver similar reagent sensitivity information as samples from patients receiving dabigatran or rivaroxaban as part of their routine care. Two laboratory sites tested commercial calibrator material for dabigatran and rivaroxaban (Hyphen Biomedical) using PT and APTT reagents and data was compared to samples collected from patients taking NOACs that were quantified by LC-MS/MS. Correlation statistics and calculating the amount of drug required to double the clotting time of normal plasma were performed. All drug calibrator material correlated more strongly (R²> 0.95) for any reagent/drug combination than patient samples (R² ranged from 0.29-0.86). Dabigatran calibrator results and patient data were equivalent for SynthASil and PTT-A APTT reagents. The dabigatran and rivaroxaban calibrator material over-estimated drug sensitivity for all PT reagents when compared to sensitivity data calculated based on drug levels obtained by LC-MS/MS from patient samples. In conclusion, drug-specific calibrators overestimated reagent sensitivity which may underestimate in vivo drug concentration in a given patient. Further studies are required to assess whether this method of determining relative sensitivity of NOAC on routine coagulation assays should be recommended.

Dabigatran effects on the international normalized ratio, activated partial thromboplastin time, thrombin time, and fibrinogen: a multicenter, in vitro study

BACKGROUND

Patients receiving the direct thrombin inhibitor dabigatran may have selected anticoagulation assays performed as part of routine care. The effect of dabigatran on the international normalized ratio (INR), activated partial thromboplastin time (aPTT), thrombin time (TT), and fibrinogen requires clarification.

OBJECTIVE

To describe the effect of dabigatran on selected assays in North America and the United Kingdom.

METHODS

Pooled normal plasma enriched with dabigatran at concentrations of 25, 50, 75, 100, 125, 150, 200, 300, 400, and 500 ng/mL were sent blinded to 19 centers in the US, the UK, and Canada to assess the effect of dabigatran on routine coagulation screening tests, the INR, aPTT, TT, and fibrinogen.

RESULTS

Data were returned from 16 centers. For effects on INR, Neoplastine CI Plus and Simplastin HTF were the most sensitive and Thromborel S the least sensitive to increasing dabigatran concentrations. For the aPTT, all reagents demonstrated decreasing sensitivity to increasing dabigatran concentrations. Measured fibrinogen either demonstrated no change or factitious decrease with increasing dabigatran concentrations. Commercial TT methods were very sensitive to low concentrations of dabigatran, with 9 of 10 reporting sites exceeding test limits at dabigatran concentrations of 100 ng/mL.

CONCLUSIONS

The INR, aPTT, and TT rise as dabigatran concentrations increase. Both the INR and aPTT increase in a linear pattern with marginal slopes, creating challenges in using these assays as reliable means for assessing the amount of dabigatran present. The commercial TT assay is very sensitive at low concentrations of dabigatran. Fibrinogen test results may be either unaffected or lower in the presence of dabigatran.