PT / INR (Clotting Time)
Also known as: Prothrombin time, INR test, PT INR test, khoon jamne ka test
Prothrombin time (PT) measures how long your blood takes to clot. INR is the same result converted to a standard scale, so it can be compared between labs.
Why it's ordered
Monitoring warfarin treatment, checking clotting before surgery or procedures, and assessing liver function or bleeding problems.
Preparation
No fasting needed. If you take warfarin, take it as usual unless your doctor says otherwise, and tell the lab your dose.
Typical adult values
| PT | about 11–13.5 seconds (lab-specific) |
|---|---|
| INR, not on warfarin | about 0.8–1.2 |
| INR target on warfarin | usually 2.0–3.0; higher for some mechanical heart valves |
Ranges vary between labs and methods. Always use the range printed on your report.
If it's high
A high INR means blood takes longer to clot. On warfarin, an INR above your target raises the risk of bleeding. Without warfarin, it can be caused by liver disease, vitamin K deficiency or clotting-factor problems.
If it's low
On warfarin, an INR below target means the dose may not be protecting you enough from clots.
Good to know
Many foods and medicines change warfarin's effect, including antibiotics, painkillers and large changes in green leafy vegetables. Never change your warfarin dose yourself; your doctor or anticoagulation clinic adjusts it. Seek urgent help for black stools, vomiting blood or severe headache.
Common questions
What is a normal INR?
Without warfarin, INR is typically about 0.8–1.2. Always use the range printed on your report.
What INR should I have on warfarin?
Usually 2.0–3.0; higher for some mechanical heart valves. Your doctor sets your personal target.
What does a high INR mean?
A high INR means blood takes longer to clot. On warfarin, an INR above your target raises the risk of bleeding.
Can food affect my INR?
Yes. Many foods and medicines change warfarin's effect, including antibiotics, painkillers and large changes in green leafy vegetables. Never change your warfarin dose yourself.