Prothrombin Time (PT) with International Normalized Ratio (INR) – Plasma-Based
This test measures how long it takes for blood to clot, using plasma from your sample. It helps assess the function of blood clotting factors, often used to monitor treatments like warfarin.
["PT/INR checks your blood’s ability to clot safely and guides treatment for conditions affecting clotting."]
Key facts at a glance
- LOINC
- 6302-4
- Short code
- Coagulation normal/actual PPP PT
- Synonyms
- Coagulation normal/actual PPP PT
- Category
- chemistry
- Sample
- plasma
- Container
- Lavender-top (EDTA) or Green-top (Heparin)
- Units
- N/A
- Ref low
- 44
- Ref high
- 147
- Critical range
- — – 5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- coag-tissue-factor-induced
- CPT
- 84075
- SNOMED
- 27550007
- 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
What Is PT/INR Testing Used For?
PT/INR tests are primarily used to evaluate the effectiveness of anticoagulant medications (like warfarin) and to diagnose or monitor bleeding disorders. It also helps detect liver disease, since the liver produces many clotting factors.
How Is the Test Performed?
A blood sample is drawn, and plasma is separated. The test measures the time it takes for the plasma to clot under controlled conditions. The INR standardizes results across different labs by comparing your PT to a normal value.
What Does a PT/INR Result Mean?
Results are reported as a PT (time in seconds) and INR (a ratio). Higher INR values (above 1.0) may indicate too much clotting risk, while lower values (below 1.0) may suggest insufficient clotting. Your doctor will interpret results based on your medical condition and treatment needs.
Common Reasons for Testing
You might have a PT/INR test if you’re on blood thinners, have liver disease, experience frequent bruising or bleeding, or are at risk for clots. It’s also used before surgeries or procedures that could affect clotting.
Reference range
Adult: 44-147 U/LN/A
No special preparation required. Avoid fatty meals before the test if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
PT/INR
Frequently asked questions
Why might my doctor order a PT/INR test?
What can affect my PT/INR results?
Do I need to prepare for 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