The international normalised ratio (INR) is a laboratory measurement of how long it takes blood to form a clot. It is used to determine the effects of oral anticoagulants on the clotting system.

Typical Target INRs

Important target International Normalised Ratios (INRs) to remember include:

• For patients with atrial fibrillation: 2-3
• For patients with metallic valve replacements:
  • aortic: 3.0
  • mitral: 3.5
• Following venous thromboembolism (VTE): 2-3

Note that for patients with a recurrent VTE whilst on Warfarin, the target INR should be increased from 2-3 to 3-4.