ADLM guidance document on coagulation testing in patients using direct oral anticoagulants

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Authors

Lindsay A.L. Bazydlo
Department of Pathology
University of Virginia 
Charlottesville, VA, United States  

Maximo J. Marin
Department of Pathology Immunology and Laboratory Medicine
Division of Infectious Diseases
University of Florida 
Gainesville, FL, United States 

Anna E. Merrill
Department of Pathology
University of Iowa 
Iowa City, IA, United States 

Louise M. Man
Department of Hematology/Oncology 
University of Virginia 
Charlottesville, VA, United States   

Olajumoke O. Oladipo
Department of Pathology and Laboratory Medicine 
Penn State Milton S. Hershey Medical Center  
Hershey, PA, United States

Neil S. Harris
Department of Pathology Immunology and Laboratory Medicine
Division of Infectious Diseases
University of Florida 
Gainesville, FL, United States  

Previous presentation: This work was presented on July 28, 2025, at ADLM 2025, Chicago, IL.
This document was approved by the Academy Content Development Committee and Academy Council in June 2025 and the ADLM Board of Directors in July 2025.
https://doi.org/10.1093/jalm/jfaf155 

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Background: Coagulation testing has an important role in the diagnosis, monitoring, and therapeutic decision-making for patients with abnormal hemostasis. As the field of anticoagulation options has expanded, the introduction of direct oral anticoagulant (DOAC) drugs has provided an option for patients utilizing drugs that do not require routine monitoring. Patients on these drugs may still need coagulation testing for prognostic purposes, and there are a number of nuances to consider when performing coagulation testing in patients who are prescribed DOACs.

Content: This document provides guidance on the tests that may or may not be impacted by the presence of DOACs in the blood. A discussion is provided about specific coagulation tests used and the impact of testing samples with a DOAC present. Options are presented to help mitigate the impact of DOACs on the testing. In addition, this document discusses how to test for and interpret DOAC concentrations in specific patient populations.

INTRODUCTION

The introduction of direct-acting oral anticoagulants (DOACs) has been a major advancement in the management of anticoagulation. Previously, outpatient oral anticoagulation was limited to vitamin K antagonists, namely warfarin. Vitamin K agonists have numerous drug-drug and dietary interactions. They also require frequent laboratory monitoring for therapeutic ranges and require dosing changes chronically. In contrast, DOACs allow for oral anticoagulation with fixed doses that have relatively predictable pharmacokinetic characteristics and do not generally require routine therapeutic monitoring. These drugs also have fewer drug–drug and drug–food interactions. In a relatively healthy patient population, the duration and efficacy of the DOACs are generally dependent on half-life, age, and renal excretion or clearance. Table 1 summarizes indications, mechanisms of action, and the pharmacokinetic properties of the DOACs (1, 2). Commercially available DOACs in the United States currently include dabigatran (Pradaxa®), rivaroxaban (Xarelto®), apixaban (Eliquis®), and edoxaban (Savaysa®). Dabigatran is a competitive direct thrombin inhibitor, while rivaroxaban, apixaban, and edoxaban are competitive direct factor Xa (FXa) inhibitors.

Table 1. Indications, mechanisms, and pharmacokinetic properties of DOACs.

Abbreviations: CAD, coronary artery disease; NVAF, nonvalvular atrial fibrillation; PAD, peripheral artery disease; VTE, venous thromboembolism.

Despite the significant improvement in anticoagulant administration, DOACs have introduced challenges for both clinical laboratorians and clinicians. Specifically, providers need to understand the impact DOACs have on diagnostic hemostasis testing. This comprehension is vital to accurately interpreting results, forming clinical impressions, and rendering sound management decisions. This document is an expert opinion and serves to provide evidence-based guidance for coagulation testing in patients who are taking DOACs. In preparing this guidance document, the focus was on the laboratory methods as the driving principle for our approach while also extracting and highlighting the most practical information in the literature to answer the following questions:

1. What is the impact of DOACs on basic hemostasis testing?
2. Which coagulation tests can be performed while a patient is on a DOAC?
3. Which coagulation tests should be avoided while a patient is on a DOAC?
4. What is the role for point-of-care (POC) testing in the presence of DOACs?
5. What strategies can be used to mitigate testing interferences in patients taking DOACs?
6. Should DOAC concentrations be monitored?
7. What tests are available for measuring DOACs?
8. How should DOAC concentrations be interpreted?

What is the impact of DOACs on basic hemostasis testing?

Basic hemostasis testing commonly consists of the prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen activity assays. These assays rely on the principle that a clot can be formed due to appropriate thrombin generation. In vivo, DOACs affect the common coagulation pathway that ultimately disrupts thrombin generation (Fig. 1) and could hypothetically impact clot-based PT and aPTT testing. From a laboratory perspective, however, this is much more complicated.

Fig. 1. A schematic illustrating the coagulation cascade in vitro. The intrinsic and extrinsic pathways intercept at FXa, which is the start of the common pathway. FXa is responsible for activating prothrombin to thrombin, and thrombin cleaves fibrinogen into fibrin, which arranges to form the fibrin clot. The anti-Xa DOACs inhibit the activity of FXa, while the thrombin inhibitor DOAC inactivates thrombin. Created in BioRender. Harris, N. (2024) https://BioRender.com/c54d428.

If the PT and/or aPTT are prolonged due to DOACs, the degree of their prolongation cannot be used to infer DOAC concentrations because of an unsuitable correlation (3–6). Further, there is variable sensitivity in testing to different DOACs that adds another layer of complexity. For example, the PT is less sensitive to apixaban than it is to rivaroxaban, and most PT reagents cannot adequately detect peak and trough levels of apixaban. On the other hand, whether DOACs will affect the PT or aPTT depends on the testing platform (i.e., the specific method, reagent lot-lot variation), the specific DOAC, drug metabolism, and drug plasma concentration (3, 5, 7, 8). Fibrinogen activity testing using the Clauss fibrinogen method is generally considered to be insensitive to DOACs, though high dabigatran concentrations may cause a false decrease for some assay reagents.

Summary

• PT and aPTT may be affected by DOACs (platform/assay dependent) and should not be used to assess DOAC presence and/or concentration.
• Fibrinogen activity measurements can generally be obtained without interference from DOACs.

WHICH COAGULATION TESTS CAN BE PERFORMED WITHOUT INTERFERENCE FROM DOACS?

The impact of DOACs varies based on the methodology used for the test. In general, methodologies not affected by the presence of DOACs include polymerase chain reaction, immunoassays, and platelet function testing. Polymerase chain reaction testing is commonly used for the detection of factor V Leiden and prothrombin gene mutations. Serology-based methods such as enzyme-linked immunosorbent assays, lateral flow immunoassays, agglutination methods, and chemiluminescent immunoassays do not rely on any type of clot formation and are unaffected by DOACs. Immunoassays are commonly used for measuring von Willebrand factor, antiphospholipid antibodies, D-dimer, protein S and C antigen, antithrombin antigen, and fibrinogen antigen.

Platelet function testing (PFT) availability varies widely between laboratories. Further, PFT can be performed on POC systems (e.g., PFA-100/200, VerifyNow™ etc.) or considered high-complexity testing (e.g., light transmission aggregometry) depending on the testing platform and method. Because PFTs do not generally rely on thrombin generation for their evaluation of platelets, they should not be affected by DOACs. The current evidence, albeit relatively limited, indicates that DOACs do not significantly affect PFT platforms (9–14). However, regarding light transmission aggregometry, specific reagent agonists used to induce platelet aggregation may be impacted by DOACs—specifically, thrombin and thrombin receptor-activating peptides (9, 10, 14–19).

Summary

• Polymerase chain reaction and immunoassays are unaffected by DOACs.
• Based on the current evidence, platelet function testing is relatively unaffected by DOACs, but specific agonists (thrombin and thrombin receptor-activating peptides) should be avoided for light transmission aggregometry.

WHICH COAGULATION TESTS SHOULD BE AVOIDED WHEN A PATIENT IS TAKING A DOAC?

In general, certain clot-based tests and some chromogenic assays should be avoided in patients taking a DOAC, as DOACs can lead to test result misinterpretation.

Should factor activity assays be avoided?

Coagulation factor activities are commonly measured using clot-based or one-stage assays. Briefly, the patient plasma is diluted with factor-deficient plasma and assayed by the PT (for factors II, V, VII, and X) or aPTT (for factors VIII, IX, XI, and XII). The measured clotting time is inversely proportional to factor activity. As described earlier, DOACs variably affect the PT and aPTT, with the degree of prolongation dependent on the assay reagent, type, and concentration of DOAC present. Therefore, factor activities determined via one-stage assays with DOAC-susceptible PT or aPTT reagents have the potential to underestimate factor activities in the presence of DOACs.
In vitro spiking studies have demonstrated that increasing concentrations of dabigatran lower PT- and especially aPTT-based factors in a concentration-dependent manner (20, 21). Of the PT-based factors, factor II may be the most affected and factor X the least affected. Misleading results can occur with dabigatran-containing samples as they often display results suggestive of a nonspecific inhibitor effect.
Increasing concentrations of rivaroxaban and apixaban can also lead to factitiously underestimated one-stage factor activities (22–25). Rivaroxaban generally has more of an effect than apixaban, which reflects the varying sensitivities of PT and aPTT reagents to these different FXa inhibitors. As with dabigatran, apixaban and rivaroxaban often induced a nonspecific inhibitor effect.
In addition to falsely lowering factor activities measured by one-stage assays, DOACs may lead to the factitious presence of factor inhibitors (20, 24).

Clot-based protein C activity. Protein C activity via clot-based assay is overestimated in the presence of rivaroxaban, edoxaban, or dabigatran but not apixaban (31, 32). Clot-based methods are generally discouraged in favor of chromogenic assays unless there is a strong clinical suspicion for the rare type II protein C deficiency (33). False elevation in protein C activity could mask true deficiency of this natural anticoagulant, delaying appropriate diagnosis and management. It is recommended that chromogenic protein C activity testing be used in the presence of DOACs.

Protein S activity. Functional testing for protein S activity can be performed via PT-, aPTT-, or Russell viper venom time (RVVT)-based clotting tests (34). aPTT- and RVVT-based protein S activity assays are exquisitely sensitive to dabigatran (20, 35). Clot-based protein S activity may also be overestimated by FXa inhibitors and is particularly sensitive to rivaroxaban (31, 36–38). False elevation in protein S activity could mask true deficiency of this natural anticoagulant, delaying appropriate diagnosis and management. It is recommended that immunoassay-based free protein S antigen testing be used in the presence of DOACs.

Activated protein C resistance (APCR). APCR assays rely on clot formation with aPTT-, RVVT-, or prothrombinase-based reagents where the patient plasma is prediluted in factor V-deficient plasma, analyzed with and without the addition of activated protein C and a ratio between these 2 clotting times calculated. Increasing APCR ratios have been observed with increasing concentrations of dabigatran, apixaban, rivaroxaban, and edoxaban, which could lead to a false normal APCR ratio in an individual who carries the factor V Leiden mutation (20, 22, 31, 35, 39). Different APCR reagents demonstrate variable susceptibility to DOAC interference, with prothrombinase- and RVVT-based assays more affected by dabigatran and aPTT-based assays less affected by apixaban (37, 39, 40). It is recommended that molecular testing be used to test for the factor V Leiden mutation in the presence of DOACs (41).

Thrombin time (TT)/dilute TT. The TT is unaffected by FXa inhibitors but is too sensitive to dabigatran to give any indication of drug concentration (21, 31, 42). However, a modification of the thrombin time, the dilute TT, demonstrates a concentration-dependent prolongation of the clotting time and, thus, is more appropriate for dabigatran quantification (43).

Reptilase time. Reptilase time measures fibrin formation following fibrinogen cleavage and fibrinopeptide A release by the batroxobin snake venom. The reptilase test is unaffected by all DOACs (20, 22, 31, 42).

Summary

• Clot-based protein C and protein S activity may be overestimated in the presence of DOACs, potentially masking true deficiency of these natural anticoagulants.
• APCR testing is susceptible to interference from DOACs, but the interference is variable depending on the reagent and anticoagulant.
• The TT and dilute TT are prolonged by dabigatran but unaffected by FXa inhibitors.

Are chromogenic assays impacted?
Relative to clot-based assays, chromogenic assays are less sensitive to interferences from DOACs. Chromogenic assays comprise 2 stages that are both independent of clot formation: activation of a serine protease capable of cleaving a specific peptide nitroanilide substrate and cleavage of the substrate to release a chromophore whose concentration is measured spectrophotometrically. Active forms of protein C, factor II, and factor X are commonly used in chromogenic reactions.

Chromogenic protein C activity. Chromogenic protein C activity assays can be reliably performed in patients taking any DOAC, since protein C is not the target of these anticoagulants and is activated directly via viper venom (21, 24, 32).

Antithrombin activity based on factor IIa. It is important to recognize that chromogenic antithrombin activity assays that rely on factor IIa (i.e., thrombin) for chromophore generation can be performed in patients taking FXa inhibitors but will be falsely elevated in patients taking dabigatran (31). Dabigatran affects thrombin-based antithrombin assays in a dose-dependent manner (20, 21, 32, 35).

Antithrombin activity based on factor Xa. Chromogenic antithrombin activity assays commonly use factor X activity for chromophore generation and can be performed in patients taking dabigatran but will be unreliable in patients taking FXa inhibitors (20, 31, 32). Different FXa-based antithrombin reagents may demonstrate varying sensitivities to the FXa inhibitors (31).

Anti-Xa activity. The use of chromogenic anti-Xa assays for therapeutic monitoring of unfractionated heparin and low molecular weight heparin is now commonplace, but the measured activity reflects all anti-Xa activity in the specimen and will be elevated in the presence of FXa inhibitors. Therefore, anti-Xa activity assays are not reliable for heparin monitoring in patients with residual direct FXa inhibitor present (44, 45).

Chromogenic factor VIII, IX and X activities. FXa inhibitors will reduce factor VIII, IX, and X activities when measured by chromogenic principles since these assays rely on factor Xa activity for chromophore generation. Plasma apixaban and rivaroxaban concentrations well within the typical on-therapy ranges for these anticoagulants may be sufficient to yield a factitiously low chromogenic factor VIII activity (31).

Factor XIII. Dabigatran can lead to falsely low levels in the chromogenic FXIII assay (6).

There are 3 general strategies that can be implemented to mitigate these known interferences, which include (a) discontinuing DOAC treatment, (b) using a different analytical method not subject to the interference, and (c) reversal or removal agents to neutralize the inhibition. In situations where testing must be performed while patients are prescribed DOACs, temporary discontinuation of the DOAC ideally should be considered using appropriate clinical judgment. Additionally, not all DOACs behave in the same manner in specific assays, and a change in methodology may be a helpful alternative. For example, the chromogenic antithrombin activity assay is available in 2 different forms; one form uses the inhibition of FXa, and the other uses the inhibition of thrombin. Direct FXa inhibitors interfere with assays using the inhibition of exogenous FXa, causing falsely increased results for antithrombin (56). In contrast, antithrombin assays that use exogenous thrombin inhibition do not show any interference from direct FXa inhibitors. The following discussion focuses on other strategies that may mitigate DOAC interference in specific assays, including a section on specific products for DOAC neutralization.

Strategies for factor assays
The underestimation of factor activity and nonspecific inhibitor effect seen in clot-based factor assays (see section 3a) may be mitigated by multidilution analysis and utilizing DOAC-insensitive reagents (32). However, these strategies have been shown to be potentially more effective for rivaroxaban and apixaban than for dabigatran.

Strategies for LA testing
Similarly to other coagulation testing, it is preferable for LA testing to be performed in the absence of anticoagulants (i.e., before the initiation of DOAC therapy) (26, 29). If therapy has been started and testing is required, an earnest consideration of temporarily stopping therapy should be evaluated. If the risk of temporary discontinuation is not excessively high, consider stopping the DOAC therapy for a minimum of 2 to 3 days before collecting the sample for LA testing (3, 28). If the risk of temporary discontinuation of anticoagulation is too high, consider a temporary transition to low molecular weight heparin, which may have less interference on the LA testing, and draw trough levels just before the next dose (3).

Strategies for DOAC neutralization
If anticoagulant discontinuation is not safe or feasible, consider the use of DOAC removal agents in sample preparation prior to performing coagulation testing. DOAC-STOPTM and DOAC-RemoveTM are products that claim to absorb or remove any DOAC in plasma samples while having a minimal effect on plasma proteins involved in the clotting mechanism and are supported by some studies such as PT, aPTT, anti-Xa, TT, and LA panels (57–61). More recently, a DOAC filter has been introduced to remove DOACs prior to LA testing (62). These assays are classified as laboratory-developed tests, which require additional resources and a thorough evaluation by the laboratory director and staff.

Similarly, the reversal agents idarucizumab and andexanet alfa may be used as a sample pretreatment step to neutralize the impact of dabigatran and factor Xa inhibitors, respectively. Idarucizumab is a monoclonal antibody fragment that binds to dabigatran with an affinity around 350 times stronger than its affinity for thrombin (63). Andexanet alfa is a recombinant modified human factor Xa decoy protein that has no catalytic activity but can bind factor Xa inhibitors with high affinity (64). Both have been shown to neutralize DOACs in samples prior to coagulation testing (65, 66).

Importantly, the approach with DOAC neutralizing agents can be cost-prohibitive and not feasible for all laboratories. Utilizing these strategies requires resources and direct discussions with laboratory leadership for an evaluation and implementation

Communication strategies for laboratories
In most cases, the strategies discussed here require communication between the laboratory and clinicians. The laboratorians have information regarding the potential interferences by DOACs on the laboratory assays, while clinicians are aware of their patient’s most current clinical context, including anticoagulation status, future anticoagulation management, and laboratory testing needs. Effective communication, exchange of information, and crafting strategies between both parties have been shown to optimize patient care (67). The level of communication between parties will likely vary and be dependent on the type of medical institution and laboratory. A simple route achievable for many laboratories could include attaching a comment to results where certain DOACs could interfere. An example is attaching a comment that reads, “Factor Xa inhibitors may lead to false increases in this test” to an antithrombin assay that uses factor Xa. A higher level of communication could include continuing medical education lectures given by the laboratory director or staff to ordering providers and/or on an individual case-by-case basis if the laboratory director is involved in coagulation test interpretations and direct communication with the clinical team. Another method could incorporate information technology to guide ordering based on a defined algorithmic approach to ultimately tailor the best available testing for the patient’s specific scenario. The aforementioned strategies may be used in combinations or in hybrid forms to satisfy individual institutional needs.

Summary

• Alternative laboratory testing methods may be considered to assist with interpreting coagulation test results when DOAC interference is involved.
• Clot-based factor and inhibitor testing should be avoided in patients taking DOACs, but if testing must be performed, multidilution analysis and use of DOAC-insensitive PT and aPTT reagents are recommended if available.
• LA testing should be performed in the absence of DOAC treatment, but if testing is necessary, multiple strategies should be considered by both the clinical and the laboratory team in collaboration.
• DOAC neutralizing reagents are available and may have some potential for their utilization. However, they are cost-prohibitive and may not be possible to implement by most laboratories.
• Multiple strategies exist for laboratories to communicate with clinicians about the impact of DOACs on coagulation testing.

SHOULD DOAC CONCENTRATIONS BE MONITORED?

DOACs have predictable pharmacokinetics and pharmacodynamics relative to warfarin with fewer interferences from food and other medications; therefore, routine monitoring is generally not necessary for dose adjustments, especially when there are no clinical concerns for toxicity or lack of efficacy (5, 7, 68–70).
There are urgent and nonurgent situations proposed where screening for the presence of DOACs may be clinically useful. Urgent situations include severe hemorrhage (toxicity) or thrombosis (therapy failure), an emergent surgical procedure while on therapy, and trauma. Nonurgent situations include advanced age, severe renal failure with dialysis dependence, prior intervention with high bleeding risk, prior small bowel resection, gastrointestinal malabsorption, patients with extremes of body weight, failed therapy, and drug interactions (9, 71–74).
It is highly discouraged to test patients beyond these very limited clinical scenarios based on the available data (75). Accordingly, due to the limited clinical utility, infrequent need, and relatively predictable pharmacokinetics and pharmacodynamics, many clinical laboratories do not perform assays that measure DOACs.

WHAT TESTS ARE AVAILABLE FOR MEASURING DOACS?

If DOAC measurement is being considered, there are indirect and direct measurements that can be strategically implemented. While widely available, the PT and aPTT are not appropriate for measuring DOACs.

Indirect measurement
Indirect DOAC assays are used to determine the presence or absence of the drug in the plasma of the patient (5, 7, 76, 77). TT is highly sensitive to dabigatran and can be used to detect the presence of dabigatran. A normal TT rules out the presence of dabigatran in a specimen. Note the TT is not affected by the FXa inhibitors. In contrast, normal PT and/or aPTT results cannot be used to definitively exclude the presence of a DOAC in a sample (3–6).
Chromogenic anti-Xa assay calibrated for unfractionated heparin and low molecular weight heparin can detect the presence of direct FXa inhibitors (7). Since anti-Xa assays are widely available, they may be useful in emergency situations to detect the presence of a factor Xa inhibitor in the patient’s plasma, though they demonstrate variable sensitivity to FXa DOACs and will not provide a DOAC concentration (78). This assay is widely available and may assist with DOAC detection (7).