INR target range (deep vein thrombosis (DVT) and pulmonary embolism (PE))

• INR 2-2.5
  
  
• prophylactic treatment for DVT (short-term)
  
  
• INR 2-3
  
  
• prophylactic treatment for hip surgery and surgery for femur fractures (short to medium term)
• treatment of venous thromboembolism - deep vein thrombosis (DVT) or pulmonary embolism (PE) (1)
  • anticoagulation for 1 month is inadequate treatment after an episode of VTE
  • at least 6 weeks anticoagulation is recommended after calf vein thrombosis and at least 3 months after proximal DVT or PE
  • for patients with temporary risk factors and a low risk of recurrence 3 months of treatment may be sufficient
  • for patients with idiopathic VTE or permanent risk factors at least 6 months anticoagulation is recommended
  • target INR of 2·5 is recommended for long-term oral anticoagulant (VKA) therapy for secondary prevention of VTE
  • target INR of 2·5 is recommended for patients with DVT or PE associated with antiphospholipid syndrome
    • target of 3·5 is also recommended for patients who suffer recurrence of VTE whilst on warfarin with an INR between 2·0 and 3·0
• cardioversion (1)
  • target INR of 2·5 is recommended for 3 weeks before and 4 weeks after cardioversion
    • to minimise cardioversion cancellations due to low INRs on the day of the procedure a higher target INR, e.g. 3·0, can be used prior to the procedure
• peripheral arterial thrombosis and grafts
  • antiplatelet drugs remain first line intervention for secondary antithrombotic prophylaxis. If long-term anticoagulation is given to patients at high risk of femoral vein graft failure a target INR of 2·5 is recommended (1)
• coronary artery thrombosis
  • if oral anticoagulant therapy is prescribed a target INR of 2·5 is recommended (1)
• systemic embolism after MI
• mitral stenosis with embolism (long term)
• atrial fibrillation (long-term) - it may be safer to aim for an INR of 2 in those aged over 75 years (3)
  • risk of stroke is 3 times greater in patients with atrial fibrillation with mitral stenosis than in those without valve disease - based on its apparent effectiveness in non-randomized studies and its effect in non-rheumatic atrial fibrillation, warfarin is usually given to maintain an INR of 2.5 (5)
    
    
• INR 3.0 or more
  
  
• treatment of recurrent DVT, PE (long term)
  • target of 3·5 is also recommended for patients who suffer recurrence of VTE whilst on warfarin with an INR between 2·0 and 3·0
• prosthetic heart valves (long-term)
  • for patients in whom valve type and location are known specific target INRs are recommended (1)
    • bileaflet valve (aortic) 2·5
    • tilting disk valve (aortic) 3·0
    • bileaflet valve (mitral) 3·0
    • tilting disk (mitral) 3·0
    • caged ball or caged disk (aortic or mitral) 3·5
  • otherwise a target INR of 3·0 is recommended for valves in the aortic position and 3·5 in the mitral position (1)

Notes (1):

• bioprosthetic valves:
  • long-term warfarin not required in absence of atrial fibrillation
  • oral anticoagulants are not required for valves in the aortic position in patients in sinus rhythm, although many centres anticoagulate patients for 3?6 months after any tissue valve implant
    • patients with bioprostheses in the mitral position should receive oral anticoagulants to achieve an INR of 2.5 for the first 3 months. After 3 months, patients with atrial fibrillation should receive lifelong therapy to achieve an INR of 2.5
    • patients with bioprosthetic valves with a history of systemic embolism and those with intracardiac thrombus should also be anticoagulated to achieve an INR of 2.5
    • patients who do not require oral anticoagulants after the first 3 months may be considered for antiplatelet therapy, e.g. aspirin
      
      
• INR values and risk of haemorrhage versus risk of thromboembolism in treatment of DVT/PE
  • risks of haemorrhage and thromboemboli are minimized at international normalized ratios of 2-3. Ratios that are moderately higher than this therapeutic range appear safe and more effective than subtherapeutic ratios (6)

Reference:

• 1. Baglin TP et al. British Committee for Standards in Haematology - Guidelines on oral anticoagulation (warfarin): third edition - 2005 update British Journal of Haematology 2006; 132 (3): 277-285.
• 2. MeReC Bulletin (1997); 8 (1): 1-4.
• 3.MeReC Bulletin (2002), 12 (5), 17-20.
• 4. MeReC Bulletin (2003); 13(4): 13-16.
• 5.British Committee for Standards in HaematologyGuidelines on oral anticoagulation: third edition British Journal of Haematology 1998;101 (2); 374-387.
• 6. Oake N et al.Anticoagulation intensity and outcomes among patients prescribed oral anticoagulant therapy: a systematic review and meta-analysis. CMAJ. 2008 Jul 29;179(3):235-44