Interpret Your Prothrombin Time / INR Results
Enter your PT/INR value below and get an instant, free AI interpretation — a plain-English explanation checked against WHO/IFCC reference ranges.
Medical Disclaimer
This AI-generated interpretation is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Results may vary based on individual health factors not captured here.
Always consult a qualified healthcare professional before making any health decisions. Read full disclaimer →
Prothrombin Time / INR Normal Ranges
Prothrombin time (PT) measures how long it takes blood to clot via the extrinsic coagulation pathway, which includes factors I, II, V, VII, and X.
| Reference Range | Unit | Notes |
|---|---|---|
| 11 – 13.5 | seconds | Prothrombin Time (PT) |
Also reported in: INR.
Critical (Panic) Values
Critical High: > 5 seconds. Values outside these limits require immediate clinical attention.
Why Doctors Order the Prothrombin Time / INR Test
PT/INR is the primary test for monitoring warfarin (Coumadin) anticoagulation therapy. It also screens for deficiencies in extrinsic pathway clotting factors, severe liver disease (where factor synthesis is reduced), and vitamin K deficiency.
How to Enter Your PT/INR Result
Prothrombin Time / INR can be reported in seconds or INR. Choose the unit printed next to your result on the lab report so it is compared with the matching reference range.
What a Low or High PT/INR Can Be Associated With
Below the reference range
- Not clinically significant (low INR or short PT is not a recognized problem)
Above the reference range
- Warfarin therapy (most common cause of prolonged INR)
- Severe liver disease (reduced factor synthesis)
- Vitamin K deficiency (malnutrition, malabsorption, antibiotics)
- Disseminated intravascular coagulation (DIC)
- Factor II, V, VII, or X deficiency (rare inherited)
These are common associations, not a diagnosis. A single result is read alongside your symptoms, history and other tests — discuss it with your doctor.
What Can Change Your PT/INR Result
Before you read too much into a result, consider whether any of these applied:
- Warfarin and other vitamin K antagonists (main reason for elevated INR)
- Antibiotics (suppress gut bacteria that produce vitamin K)
- Dietary vitamin K changes (green leafy vegetables lower INR)
- Many medications interact with warfarin (amiodarone, fluconazole, metronidazole raise INR)
Preparing for the test: For routine coagulation testing: no special preparation. For warfarin monitoring: test at the same time of day consistently.
Symptoms That Often Prompt PT/INR Testing
- Easy bruising
- Excessive bleeding after cuts or procedures
- Heavy menstrual periods
- Blood in urine or stool
- Gum bleeding
Want the full clinical guide to Prothrombin Time / INR?
Reference ranges, causes, symptoms, preparation, and FAQs.