Coagulation
INR
LOINC 6301-6 · ratio
Ranges
Reference range: 0.8–1.2 ratio
What it is
INR (international normalized ratio) is a standardized version of the prothrombin time, so clotting results compare across labs.
Why it matters
It is the main test for monitoring the blood thinner warfarin and for assessing clotting and liver function.
What high values can mean
A higher value means blood is taking longer to clot — intended on warfarin, but too high raises bleeding risk.
What low values can mean
A lower value means faster clotting; on warfarin this can mean less protection against clots.
How to improve it
On warfarin, consistent diet (especially vitamin K), medications and regular testing keep INR in your target range.
Food & lifestyle
Keep vitamin-K-rich foods (leafy greens) consistent rather than avoiding them if you take warfarin; sudden changes shift INR.
Preparing for the test
A blood test; fasting is not required — follow your lab's instructions.
When to talk to a doctor
Discuss an out-of-range INR with your doctor promptly if you take a blood thinner.
Related markers
Sources
- MedlinePlus (NIH)
- Testing.com (AACC)
Content reviewed on June 26, 2026
Medical disclaimer
This content is for educational purposes only. It is not medical advice and does not diagnose, treat, or prevent any condition. Reference ranges vary between laboratories — always use the range printed on your report and discuss your results with a healthcare professional.
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