Test guide
Prothrombin Time / INR (PT/INR)
A clotting test measuring the extrinsic pathway, standardised internationally as INR to monitor vitamin K antagonist therapy and assess bleeding risk.
What it is for
Monitors warfarin therapy intensity, screens for coagulation factor abnormalities in bleeding or bruising workups, and assesses liver synthetic function. The INR conversion makes results comparable between laboratories with different reagent sensitivities.
Limitations
Requires properly filled citrate tubes; under-filled tubes and elevated haematocrit distort results. INR standardisation applies to vitamin K antagonists and does not transfer cleanly to direct oral anticoagulants. Point-of-care and laboratory INR can differ slightly; clinical decisions should use one consistently.
Before you test
For patients on anticoagulants, note the dose and time of the last intake. Avoid under-filled blood collection tubes.
Health information only. This guide does not diagnose or replace advice from a healthcare professional.
Also known as
- PT
- INR
- prothrombin ratio
Reviewed products
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