Is a normal Thromboelastography (TEG) result sensitive for Direct Oral Anticoagulants (DOACs) and Non-Vitamin K Antagonist Oral Anticoagulants (NOACs) unlike Prothrombin Time/International Normalized Ratio (PT/INR)?

Normal TEG is Not Reliably Sensitive for Detecting DOACs and NOACs Unlike PT/INR

A normal Thromboelastography (TEG) result is not reliably sensitive for detecting Direct Oral Anticoagulants (DOACs) and Non-Vitamin K Antagonist Oral Anticoagulants (NOACs), and should not be used as the primary test to rule out their presence. The 2023 World Journal of Emergency Surgery guidelines specifically state that there is not enough evidence to support the routine use of TEG in assessing anticoagulant exposure 1.

Limitations of TEG for DOAC/NOAC Detection

• Standard TEG parameters often remain within normal limits despite the presence of DOACs, with studies showing TEG identified coagulopathy in only 50% of patients on dabigatran and even fewer on other anticoagulants 1.
• TEG performs better at detecting DOACs at peak concentrations but loses sensitivity for detecting residual drug activity, making it unreliable for clinical decision-making about anticoagulant reversal 1.
• Kobayashi et al. found that median values for R time, alpha angle, and maximum amplitude (MA) were within normal limits and did not differ significantly between different DOACs, despite their presence 1.

Preferred Testing Methods for DOACs/NOACs

• The 2023 WSES guidelines strongly recommend performing routine coagulation assays including Activated Partial Thromboplastin Time (aPTT), Thromboplastin Time (TT), Prothrombin Time (PT), INR, and anti-Xa levels to assess anticoagulant exposure in trauma settings 1.
• For dabigatran (a direct thrombin inhibitor), the Thrombin Time (TT) is extremely sensitive and a normal TT reliably excludes clinically relevant dabigatran levels 1.
• For factor Xa inhibitors (rivaroxaban, apixaban, edoxaban), anti-Xa assays calibrated with the drug of interest are the preferred tests for quantitation 1.

Conventional Coagulation Assays vs. TEG

• Conventional coagulation assays (CCA) identified a greater proportion of coagulopathy for patients on pre-injury anticoagulation therapy compared to TEG 1.
• Ali et al. found that CCA demonstrated prolongation of INR or aPTT in 67% of patients on anticoagulation therapy, while TEG was much less sensitive 1.
• aPTT values exceeded the threshold for coagulopathy in 100% of patients on dabigatran, PT-INR in 85% of VKAs patients, and 63% of patients on anti-Xa inhibitors 1.

Specific Effects of DOACs on Coagulation Tests

• Dabigatran prolongs aPTT in a concentration-dependent but non-linear manner, especially at higher concentrations (≥200 ng/mL) 1, 2.
• Rivaroxaban prolongs PT in a dose-dependent manner, but this effect varies based on different thromboplastins due to their differing sensitivities 1.
• Apixaban and edoxaban have minimal effects on PT and aPTT, with PT potentially remaining normal at therapeutic concentrations 1.

Advanced Testing Options

• For more accurate assessment, specialized tests such as diluted thrombin time (dTT), ecarin clotting time (ECT), and calibrated anti-Xa assays provide better quantification of DOAC levels 1.
• These specialized tests are more accurate but have limited availability in emergency settings due to their complexity, cost, and longer turnaround time 1.

Recent Developments in TEG Technology

• Newer TEG systems (TEG 6s) with specialized assays (DTI assay and Anti-Factor Xa assay) have shown improved sensitivity (≥92%) and specificity (≥95%) for detecting DOACs 3, 4.
• However, these specialized TEG assays are not yet widely available or validated for routine clinical use 4.

Clinical Implications

• Relying solely on a normal TEG to exclude DOAC presence could lead to missed detection of anticoagulant effects, potentially resulting in inadequate reversal in emergency situations 1, 5.
• For trauma patients or those requiring emergency surgery, conventional coagulation tests remain the recommended first-line approach for detecting anticoagulant effects 1.

In conclusion, while TEG provides valuable information about overall clot formation and strength, it should not be used as the primary test to exclude the presence of DOACs/NOACs. Conventional coagulation tests and specialized assays remain more reliable for detecting these medications.