Table 1.
Test | Range | Components Tested | Medications |
---|---|---|---|
Prothrombin Time (PT/INR) | 12–13 sec/0.8–1.2 | Tissue factor pathway and common pathway (II, VII, X) | Warfarin, anti-Xa agents (rivaroxaban*, apixaban*, edoxaban*) |
Partial Thromboplastin Time (PTT) | 30–60 seconds | Contact activation and common pathways (all factors except factor VII) | Heparin, factor II inhibitors (dabigatran**) |
Anti-Xa Assay | 0.0 | Factor X | LMWH, anti-Xa agents (rivaroxaban*, apixaban*, edoxaban), fondaparinux |
Thrombin Time | 12–14 seconds | Factor II activity | Factor IIa inhibitors (dabigatran) |
Ecarin Clotting Time (ECT) | 22.6 to 29.0 seconds At trough: >3x the upper limit of normal suggests bleeding risk |
Factor II activity | Factor IIa inhibitors (dabigatran) |
PT/INR, prothrombin time/international normalized ratio; LMWH, low-molecular-weight heparin.
PT is frequently elevated with these agents but a prediction as to the degree of anticoagulation is unreliable with these agents.
PTT is useful in determining the presence of an anti-factor II activity, however it cannot be used to monitor the degree of anticoagulation produced by these medications.