What is a normal INR, and what is the target?
In someone not taking warfarin, INR is around 1.0. Warfarin deliberately raises it so the blood clots more slowly. For most conditions the target range is 2.0–3.0; some situations (such as certain mechanical heart valves) use a higher range.
Too low and the warfarin may not protect against clots; too high and there is a greater risk of bleeding — which is why regular monitoring and dose adjustment are needed.
What can change my INR?
Many things affect INR: other medicines and antibiotics, big changes in diet (especially green leafy vegetables, which contain vitamin K), alcohol, illness, and herbal remedies. Cranberry juice and St John's Wort are well-known culprits.
Tell any prescriber that you take warfarin, and do not start or stop other medicines or supplements without checking. Newer anticoagulants (DOACs) do not need INR monitoring.
Common questions
What does a high INR mean?
It means your blood is taking longer to clot than intended, raising bleeding risk. Your clinic will advise on adjusting the warfarin dose and, if very high, may take further action.
Why do some people not need INR checks?
The newer anticoagulants (apixaban, rivaroxaban, edoxaban, dabigatran) work in a more predictable way and do not require routine INR monitoring, unlike warfarin.
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