Monitoring of warfarin

Monitor warfarin therapy by measurement of the international normalised ratio (INR). Measure the INR daily or every second day at the start of therapy, and approximately every 4 to 6 weeks during stable chronic therapy. The frequency of monitoring depends on the INR stability, whether there is a need to vary the INR (eg to allow an invasive procedure) and the influence of concurrent illnesses and therapies.

For the management of patients who are bleeding or have a high INR, see Bleeding and overanticoagulation in patients taking warfarin therapeutically.

For patients with a persistently high or labile INR, reassess the suitability of ongoing warfarin therapy and consider an alternative anticoagulant.

Patients who have a stable INR can use point-of-care devices for self-monitoring (see Self-monitoring of warfarin).