Which lab tests can be ordered to determine DOAC activity levels?
- Drug-specific serum levels to precisely test for DOAC levels are not commonly available, and thresholds of clinically significant cut-off values have not been validated with prospective trials
- Clinician understanding of assays available in local healthcare facilities is important to ensure appropriate result interpretation; consider consultation with laboratory pathologist
- Direct thrombin inhibitors:
- Prothrombin Time (PT) and International Normalized Ratio (INR) – not useful
- Activated Partial Thromboplastin Time (aPTT)
- When prolonged implies drug presence (highly specific)
- If normal, cannot exclude drug presence
- Thrombin Time (TT) or Dilute Thrombin Time (dTT; Hemoclot®)
- When prolonged drug is present, even if a trivial amount
- If normal, definitively excludes drug presence (highly sensitive)
- Factor Xa inhibitors:
- PT/INR
- Rivaroxaban, edoxaban – When prolonged implies drug presence (specific); if normal, cannot exclude drug presence
- Apixaban – if normal, cannot exclude drug presence
- aPTT – not useful
- Anti-Xa Level*
- Level for factor Xa inhibition, specific for the anticoagulant used
-
- A positive test indicates that even a trivial amount of drug is present
- A negative test firmly rules out the presence of factor Xa inhibitor (sensitive test)
-
- *If drug-specific levels are not available, a negative test using unfractionated heparin or low-molecular weight heparin-calibrated assays rule out drug presence; a positive test indicates that drug is present
- Level for factor Xa inhibition, specific for the anticoagulant used
- PT/INR
Relative effect of DOAC presence in the plasma on commonly available coagulation assays, which yield qualitative results
|
Direct Thrombin Inhibitors |
Factor Xa Inhibitors |
||
Assay |
Dabigatran |
Apixaban |
Edoxaban |
Rivaroxaban |
PT/INR |
+/- |
+/- |
+/- |
++ |
aPTT |
++ |
- |
- |
- |
TT or dTT |
+++ |
- |
- |
- |
Anti-Xa Level |
- |
+++ |
+++ |
+++ |
+ implies a prolonged/abnormal value; - implies a normal value
References:
- Douxfils J, Ageno W, Samama CM, et al. Laboratory testing in patients treated with direct oral anticoagulants: a practical guide for clinicians. J Thromb Haemost. 2018;16:209-219.
- Samuelson BT, Cuker A, Siegal DM, et al. Laboratory assessment of the anticoagulant activity of direct oral anticoagulants: a systematic review. Chest. 2017;151:127-138.