Anticoagulation Management

Introduction to Anticoagulation Therapy

• A subtherapeutic INR (<2.0) in a patient on warfarin indicates inadequate anticoagulation and increased risk of thromboembolism, according to the European Heart Journal and Circulation 1, 2
• The American College of Cardiology recommends target INR ranges for patients with mechanical valves, with a target INR of 2.5-3.5 for mitral valves and 2.0-3.0 for aortic valves, and 2.0-3.0 for patients with atrial fibrillation 1, 3, 4

Dose Adjustment and Monitoring

• For confirmed subtherapeutic INR, the European Heart Journal and Circulation recommend increasing the warfarin dose by 10-20% and rechecking INR within 3-5 days to assess response 1, 2
• High-risk patients may require bridging with heparin or low molecular weight heparin (LMWH) until therapeutic INR is achieved, and heparin/LMWH overlap should be continued for 4-5 days until warfarin has produced the desired therapeutic response, according to the European Heart Journal, Circulation, and the American College of Cardiology 1, 2, 3

Target INR Ranges and Outcomes

• Subtherapeutic INR in mechanical valve patients significantly increases thromboembolic risk, and the American College of Cardiology recommends considering adding low-dose aspirin (75-100 mg) if recurrent embolic events occur despite therapeutic INR 1, 3
• The American College of Cardiology recommends target INR ranges to minimize the risk of thromboembolic events, with a target INR of 2.5-3.5 for mitral valves and 2.0-3.0 for aortic valves 1, 3

Special Considerations

• The European Heart Journal, Circulation, and the American College of Cardiology recommend avoiding excessive dose increases, considering medication interactions, and assessing for changes in vitamin K intake that may affect INR 1, 2, 3
• The International Society on Thrombosis and Haemostasis (ISTH) recommends investigating for the presence of anticoagulant lúpico in patients with elevated prothrombin time (TP) but normal International Normalized Ratio (INR) 5

• The following tests are recommended for diagnosing anticoagulant lúpico:

  Test	Description
  dRVVT	diluted Russell's viper venom time
  TTPA	activated partial thromboplastin time with confirmation test
  Integrated tests	screening and confirmation in one procedure

• Evaluating liver function is recommended, as liver disease can affect coagulation, and the ISTH recommends considering direct oral anticoagulants (DOACs) such as apixaban instead of vitamin K antagonists for patients who require anticoagulation 5, 7
• If anticoagulant lúpico is confirmed, monitoring with thromboplastins that are less sensitive to anticoagulant lúpico is recommended, and measuring factor X activity can be used as an alternative to INR monitoring 5
• The ISTH recommends that most procedures are safe with a normal INR, even with elevated TP, and correction of a normal INR is not necessary before invasive procedures, unless there is a history of bleeding 5, 8, 9
• Point-of-care devices for INR measurement should be avoided in patients with anticoagulant lúpico, and ensuring that the ISI of the instrument is correctly calibrated is also recommended 5