The APTT, if measured with certain reagents, is more responsive to dabigatran but much less responsive to rivaroxaban, apixaban, or edoxaban.
Dabigatran and the oral factor Xa inhibitors prolong APTT in a dose-dependent manner. In general, the APTT is more sensitive to dabigatran.
Among the oral factor Xa inhibitors, the APTT is more sensitive to rivaroxaban and edoxaban than apixaban. The APTT may remain normal in the presence of clinically relevant NOAC levels, depending on the reagent's sensitivity. The APTT cannot be relied upon as a screening test to exclude the presence of clinically significant drug levels.
A normal APTT does not exclude the presence of a therapeutic drug, nor does it exclude patients who have above therapeutic levels of apixaban.
The APTT can be measured in a clinical laboratory using a variety of commercial preparations that, because of the source of their reagents and phospholipid composition, show varied responsiveness to NOAC. Furthermore, normal or shortened APTT due to high FVIII levels or other causes could mask the effect of NOAC.
If APTT is used for patients on NOAC, results should be expressed as the ratio of patient-to-normal clotting time. When interpreting results of the APTT in patients on NOAC, it should be considered that the test might be prolonged because of coagulation defects other than those stemming from the drug taken by the patients.
