5.3. Laboratory Measurement
In the anticoagulated patient who presents with clinically relevant bleeding or needs an urgent unplanned procedure, measurement of anticoagulant activity is a key step in the evaluation. A prothrombin time (PT) and/or an activated partial thromboplastin time (aPTT) should be requested in all such patients. Interpretation of the PT and aPTT as well as the potential need to request specialized coagulation tests will depend on the clinical situation, the anticoagulant, and test availability.
Unless a concomitant defect in coagulation (e.g., disseminated intravascular coagulation) is suspected, patients taking VKA may be evaluated with the PT/ International Normalized Ratio (INR). The INR may be used to guide perioperative or bleeding management.
Laboratory measurement of the anticoagulant activity of the DOACs is more complex. The best assays are specialized and are not widely available. More accessible tests such as the PT and aPTT have important limitations. Suggestions for laboratory measurement of the DOACs based on specialized assay availability are summarized in Tables 2 and 3 (15,16).
