Blood and lab tests
What Does INR Mean on a Blood Test?
INR (International Normalized Ratio) · say it: eye-en-ARAlso written: international normalized ratio, PT/INR, prothrombin time
Short answer
INR is a standardised measure of how long your blood takes to clot, often used to check blood-thinning medicines such as warfarin.
What it means
The test starts with the prothrombin time (PT), the number of seconds a blood sample takes to clot after a chemical is added. Because PT varies between labs, it is converted into the INR so results can be compared anywhere.
A higher INR means blood is taking longer to clot. People taking warfarin have their INR checked regularly, and their doctor sets a target range for them that may differ from the usual reference range.
INR is also used before surgery and to assess liver function, since the liver makes many of the proteins needed for clotting.
Where you may see it
- Coagulation or clotting tests
- Warfarin monitoring (anticoagulation clinic) reports
- Pre-surgery and liver assessments
📄 How it looks on a report
INR 2.6
🙅 What it does not mean
- A high INR is not automatically a problem; for people on warfarin, a raised INR is often the intended goal.
- The usual reference range on the report may not be your personal target if you take a blood thinner.
- INR does not measure the effect of every blood thinner; some newer ones are not monitored this way.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “INR (International Normalized Ratio)”
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💊 Medicines whose labels mention “INR (International Normalized Ratio)”
Plain-English explanations of each medicine, from its official FDA label.
- Amoxicillin
a penicillin-class antibacterial medicine that works against bacteria
- Amoxicillin and Clavulanate Potassium
A penicillin-class antibacterial combined with a beta-lactamase inhibitor, as the label describes it
- Cephalexin
a cephalosporin antibacterial medicine (an antibiotic that treats bacterial infections)
- Escitalopram
a selective serotonin reuptake inhibitor (SSRI), a type of antidepressant
- Ivermectin
An antiparasitic medicine, sometimes called a worm-killing medicine (anthelmintic), that the FDA lists as an antiparasitic and pediculicide
- Levofloxacin
an antibiotic of the fluoroquinolone type
- Metronidazole
An antimicrobial medicine of the nitroimidazole type, used to treat certain bacterial and parasitic infections
- Omeprazole
a proton pump inhibitor (PPI), a type of medicine that lowers the amount of acid in the stomach
- Pantoprazole
a proton pump inhibitor (PPI), a medicine that reduces the amount of acid the stomach makes
- Paroxetine
A selective serotonin reuptake inhibitor (SSRI), a type of antidepressant medicine
🔗 Read more from trusted sources
- “INR (International Normalized Ratio)” on MedlinePlus ↗
US National Library of Medicine
- MedlinePlus lab test guides ↗
US National Library of Medicine
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