International normalised ratio monitoring in the community populations of the Auckland and Northland regions of New Zealand: time in therapeutic range and frequency of testing.

Background: Warfarin remains a commonly used anticoagulant for the treatment and prevention of thrombosis. To balance the risks and benefits of therapy, monitoring of the international normalised ratio (INR) is necessary. Patients derive most benefit from warfarin when they spend ≥65% of time in the therapeutic range (INR 2-3).