Information about a laboratory test
A high INR indicates slower clotting. In people taking warfarin, an INR above the usual non-anticoagulated range may be intentional; targets depend on indication and medication changes require clinical supervision.
The INR test measures the standardized ratio derived from prothrombin time so results can be compared across methods and laboratories.
It may be ordered to investigate abnormal bleeding or clotting, assess coagulation before procedures, or monitor selected anticoagulant therapies.
A low INR may mean that a person taking warfarin is below their intended target, but targets vary by indication and the result should not be used alone to change medication.
A high INR indicates slower clotting. In people taking warfarin, an INR above the usual non-anticoagulated range may be intentional; targets depend on indication and medication changes require clinical supervision.
Start with the performing laboratory's reference interval, unit, specimen type and method. Numeric information on this page is stored as sourced example intervals or clinical thresholds.
>= 0.8 – <= 1.1 ratio
Example INR interval without warfarin
This is sourced reference/clinical-context information and should not be used alone as a diagnosis or treatment decision. The laboratory report, medication use and clinical context take priority.
>= 2 – <= 3 ratio
Common warfarin INR target context
This is sourced reference/clinical-context information and should not be used alone as a diagnosis or treatment decision. The laboratory report, medication use and clinical context take priority. Warfarin dose must not be changed by the patient based on this table.
Reference ranges may vary by laboratory, method used, age, sex, pregnancy status, and clinical context. The reference range on your own laboratory report takes precedence.
The meaning of INR changes substantially with anticoagulant use. During warfarin therapy, target range depends on the individual indication and patients should not adjust doses on their own.
Prothrombin Time Test and INR (PT/INR) — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · PT/INR purpose, anticoagulation and coagulation interpretation · Verified: Aug 12, 2026
Prothrombin time (PT) — U.S. National Library of Medicine (MedlinePlus)
Government medical encyclopedia · 2025 · Example PT and INR intervals and common warfarin target context · Verified: Aug 12, 2026
Partial Thromboplastin Time (PTT) Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2026 · aPTT/PTT purpose, prolonged and shortened result context · Verified: Aug 12, 2026
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