Prothrombin Time (PT) with International Normalized Ratio (INR) - Serum
This test measures how long it takes for blood to clot, helping assess blood clotting function and detect issues like bleeding disorders or clotting problems.
["PT/INR helps monitor blood thinners and check for clotting abnormalities."]
Key facts at a glance
- LOINC
- 24171-1
- Short code
- PV2 NAb sp1 Titr Ser Nt
- Synonyms
- PV2 NAb sp1 Titr Ser Nt
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- neut
- 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 Is Done
Your doctor may order a PT/INR test to evaluate how well your blood clots normally. It’s often used to monitor medications like warfarin (Coumadin) that prevent blood clots. It can also help diagnose conditions that affect clotting, such as liver disease or bleeding disorders.
How the Test Works
A small amount of your blood is drawn and mixed with a special solution. The time it takes for a clot to form is measured and compared to a standard reference. The INR converts this time into a standardized value for interpretation.
What to Expect Before the Test
No special preparation is needed unless your doctor instructs otherwise. You may be asked to avoid certain medications or foods that could affect clotting, such as vitamin K-rich foods (like leafy greens) if you’re on blood thinners.
What to Expect During the Test
The test involves a quick blood draw from a vein in your arm. You may feel a small pinch, but it usually takes only a few minutes. The blood is sent to a lab for analysis.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
High PT/INR levels may indicate bleeding disorders, liver disease, or excessive use of blood-thinning medications. Low levels could suggest clotting problems or vitamin K deficiency. Monitoring PT/INR is critical for patients on anticoagulant therapy to prevent excessive bleeding or clotting.
Short name
PT/INR
Frequently asked questions
What does a high PT/INR mean?
What does a low PT/INR mean?
Can diet affect PT/INR results?
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