From the Guidelines
NOACS do not significantly affect PT or aPTT in a clinically meaningful way, and these tests should not be used to assess the anticoagulant effect of NOACs.
Expected Impact on Coagulation Tests
- Dabigatran: has a curvilinear relationship with aPTT, and a normal aPTT does not exclude dabigatran levels in the 'on therapy' range, but excludes drug levels above the 'on therapy' range when a sensitive assay is used 1.
- Apixaban, Edoxaban, and Rivaroxaban: may have some effect on PT, but this is not a reliable method for assessing anticoagulation intensity 1.
Measurement of Anticoagulant Effect
- Specific coagulation assays: such as diluted thrombin time (dTT) and chromogenic anti-FXa assays, are available to measure the anticoagulant effect of NOACs, but may not be routinely available in most hospitals 1.
- Point-of-care tests: should not be used to assess the anticoagulant effect of NOACs, as they are not accurate for these medications 1.
Clinical Implications
- NOACs do not require routine monitoring of coagulation: neither the dose nor the dosing intervals should be altered in response to changes in laboratory coagulation parameters 1.
- Emergency situations: may require quantitative assessment of the drug exposure and the anticoagulant effect, but this should be done using specific coagulation assays, not routine coagulation tests 1.
From the Research
Effect of NOACS on PT and aPTT
- The routine coagulation tests, including prothrombin time (PT) and activated partial thromboplastin time (aPTT), have variable sensitivities to Non-Vitamin K Antagonist Oral Anticoagulants (NOACs) 2.
- NOACs are known to affect established coagulation point-of-care tests, but specific point-of-care tests for NOACs are not available 3.
- The CoaguChek point-of-care test strongly correlated with rivaroxaban concentrations, but did not accurately detect dabigatran or apixaban, and was superior to predictions based on normal PT and aPTT values 3.
- PT and aPTT values may not accurately reflect the anticoagulant effect of NOACs, and specialized assays are recommended for laboratory measurement of NOAC levels 2, 4.
Clinical Implications
- In emergency situations, such as severe bleeding or stroke, measurement of NOAC levels may be useful to guide clinical decision making 2, 4.
- Regular monitoring of NOAC levels is not recommended, but may be beneficial in specific circumstances, such as severe bleeding or before urgent surgery 2, 4.
- The availability of NOAC-specific reversal agents may change management practices in emergencies 4.