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International normalized ratio (INR)
Make it clearer
The INR, or international normalized ratio, is the number used to monitor people treated with vitamin K antagonists, a type of oral anticoagulant.
The INR is derived from another test: the prothrombin time. That time is measured in seconds and is literally how long plasma, the liquid part of blood, takes to form a clot when calcium and tissue thromboplastin are added; tissue thromboplastin is a substance that triggers clotting through what is called the extrinsic pathway.
The problem is that this number in seconds does not mean the same thing everywhere: it changes with the instrument and with the reagent each laboratory uses. That is why it is converted into the INR. It is the same clotting stopwatch, just on a scale that laboratories share. In someone without health problems, the INR is usually 1.1 or below.
In brief
The INR is the preferred measure for monitoring people treated with vitamin K antagonists, a type of oral anticoagulant.
It is derived from the prothrombin time, which measures in seconds how long plasma takes to form a clot when calcium and tissue thromboplastin are added to activate the extrinsic pathway.
It is standardized because instruments and reagents vary between laboratories; in a person without health problems it is usually 1.1 or below.
It is the same clotting stopwatch, just on a scale that laboratories share.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingInternational Normalized Ratio: Assessment, Monitoring, and Clinical Implications, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated