Prothrombin Time and INR (PT/INR)
Reviewed
PT measures clotting time, while INR standardises PT reporting to improve comparison between laboratories and methods.
Preparation and collection
Tell the clinician about anticoagulants, other medicines, supplements, recent illness, and diet changes. Never change warfarin or another anticoagulant based only on this page.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- INR targets are indication-specific and patient-specific.
- Medicines, antibiotics, illness, alcohol, diet, supplements, liver disease, and collection problems can affect results.
What to do next
The responsible team may repeat testing, assess bleeding or clotting risk, review interactions, and adjust treatment according to a formal protocol.
Evidence source
U.S. National Library of Medicine: Prothrombin Time and INR (PT/INR)