Medical abbreviation:
INR
Type:
Blood test
Definition:
This blood test is used to measure the pro-thrombin time. This is the time taken for blood to clot. For the purposes of making warfarin prescribing easier, the figure is given as a ratio, called the International Normalised Ratio (INR). A normal (someone not on warfarin or any other similar anti-coagulant) INR is 1.0. The higher the INR, the longer it takes the blood to clot.
When would I need this test?
Doctors use the INR to help prescribe the correct dose of drugs like warfarin. Warfarin helps to “thin” the blood, helping to prevent clots by increasing the time it takes the blood to clot. Depending on the condition being treated there are different target INR ranges. For the treatment of deep vein thrombosis, the aim of warfarin therapy is to reach an INR between 2.0 and 3.0. For patients with metal heart valves, the treatment INR range is usually 2.5 to 3.5. In some patients higher INR ranges may be required.
Important
Many drugs and some foods can affect your INR, always let your doctor know if you are taking any new medication.
