What is this test?
PT measures clotting through the tissue-factor pathway, while INR standardizes the result mainly for monitoring vitamin K antagonist treatment such as warfarin. It also changes with some clotting-factor, liver or vitamin K problems.
Why might it be ordered?
- To monitor warfarin or another vitamin K antagonist.
- To investigate unexpected bleeding or assess selected liver and clotting concerns.
What sample is needed?
A blood sample is required. The laboratory chooses the correct tube and handles the sample for this test.
How should you prepare?
Take medicines exactly as directed and report the dose and time of your last anticoagulant. Do not change or skip a dose because of this test unless your treatment team instructs you to.
How should you understand the result?
The target INR for anticoagulant treatment is individual and is not the same as the reference interval for someone not taking warfarin. Contact the treatment team about results outside your agreed target.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.