Prothrombin Time (PT) with International Normalized Ratio (INR) – Plasma
This test measures how long it takes for your blood to clot, helping assess your blood’s ability to stop bleeding. It’s often used to monitor treatments for conditions affecting blood clotting.
["PT/INR checks blood clotting function and is critical for managing conditions like bleeding disorders or blood thinners."]
Key facts at a glance
- LOINC
- 6000-4
- Short code
- PA PRP Thrombin
- Synonyms
- PA PRP Thrombin
- Category
- hematology
- Sample
- plasma
- Container
- Lavender-top (EDTA) or Green-top (Heparin)
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- aggregometry-thrombin-induced
- CPT
- 85610
- SNOMED
- 396252006
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters for Your Health
Your PT/INR test evaluates the time it takes for your blood to clot, which is influenced by several clotting factors in your plasma. This is done using a standardized method to compare your results to a normal range. The INR adjusts your PT result based on the lab’s specific reagents to ensure consistency across different testing sites.
How the Test Works
A small sample of your blood is mixed with a special solution that triggers clotting. The time it takes for a clot to form is measured. The INR is calculated to normalize this time relative to a standard reference population.
Common Reasons for Testing
Doctors may order a PT/INR test to diagnose bleeding disorders, evaluate liver function (since the liver produces clotting factors), or monitor medications like warfarin (a blood thinner). It’s also used before surgeries to ensure safe clotting levels.
What to Expect Before the Test
No special preparation is needed, but you may be asked to avoid certain medications (like blood thinners) if your doctor directs it. Fast your blood for 8–12 hours before testing if instructed, though this is less common for routine PT/INR checks.
Reference range
INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A
Inform your healthcare provider if you are taking blood thinners. No special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
PT/INR
Frequently asked questions
What does a high or low PT/INR result mean?
How often should I get this test?
Can I eat or drink before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy