International Normalised Ratio (INR)

A way of measuring how fast the blood clots when the patient is taking a VKA. The prothrombin time of the patient is compared to the prothrombin time of a control blood sample and expressed as a ratio, which is then transformed into an international normalised ratio to take account of the reagent used.

This measurement is used to monitor the adequacy of anticoagulation for patients who are on VKA treatment.

See ‘monitoring’, ‘self-monitoring’ and ‘self-management’.