What is an INR test in association with Warfarin?
23rd January 2001 Warfarin is an important drug used as the mainstay of long-term anticoagulant therapy. Warfarin has a chemical structure which is similar to vitamin K and thus competitively inhibits the enzyme epoxide reductase, so limiting the active form of the vitamin to form clotting factors, especially prothrombin. Individual responses to warfarin therapy are varied and as the dosage for the treatment of patients is critical, it is important to determine the effect of the drug on anticoagulation for each patient. A standard coagulation test routinely performed in haematology laboratories is prothrombin time (PT), and this test is repeated until stabilisation occurs. The international normalised ratio (INR) is the widely recommended form of reporting prothrombin time when measuring warfarin effects. Usually the patients PT is determined along with that for a control sample of plasma and the two values are reported as a ratio. However recent studies have indicated a degree of vari
