Indications for warfarin therapy and PT/INR testing

While hemostasis is necessary for survival, the pathological formation of a blood clot, or thrombosis, poses significant health risks.

The main indications for a patient to receive vitamin K antagonists (VKAs) are the following:

  • Mechanical Heart Valves
  • Atrial Fibrillation
  • Deep Vein Thrombosis and Pulmonary Embolism
  • Myocardial infarction
  • Acute Ischemic Stroke

Oral anticoagulants are effective for primary and secondary prevention of venous thromboembolism, for prevention of systemic embolism in patients with prosthetic heart valves or atrial fibrillation, for prevention of acute myocardial infarction (AMI) in patients with peripheral arterial disease and in men otherwise at high risk, and for prevention of stroke, recurrent infarction, or death in patients with AMI.

Some physicians are reluctant to prescribe warfarin, in part because they are not familiar with techniques for administering the drug safely and fear that the drug will cause bleeding. Patients treated with warfarin do require close monitoring to avoid bleeding, but it has been shown that the drug prevents 20 strokes for every bleeding episode it causes. For most of these indications, a moderate anticoagulant intensity (INR 2.0 to 3.0) is appropriate.