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Prothrombin Time (PT) with International Normalized Ratio (INR) – Plasma

Published: August 9, 2026Updated: August 16, 2026

This test measures how long it takes for your blood to clot, helping assess blood clotting function and identify potential bleeding or clotting disorders.

Quick summary

["PT/INR helps doctors monitor conditions like liver disease or blood thinners."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
100715-2
Short code
Prothipendyl SerPl-mCnc
Synonyms
Prothipendyl SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 check if your blood is clotting properly. Common reasons include evaluating liver health, diagnosing bleeding disorders, or monitoring medications like warfarin that affect clotting. It’s also used before surgeries or procedures that might cause bleeding.

How the Test Works

A small blood sample is taken from your arm and sent to a lab. The test measures the time it takes for blood to clot after mixing with a specific chemical. The INR compares your result to a standard to ensure consistency across labs.

What to Expect Before the Test

No special preparation is needed, but inform your doctor about any medications (like blood thinners) or recent injuries that could affect results. Avoid eating or drinking anything for 10 hours before the test if instructed.

Possible Results and Interpretation

Results are reported as a PT time and INR value. Higher PT/INR times may indicate slower clotting (possible bleeding risk), while lower values could suggest faster clotting (possible clotting disorders). Your doctor will interpret results in the context of your health and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

PT/INR

Frequently asked questions

What does a normal PT/INR value mean?
A normal PT/INR varies by lab and patient factors, but generally, a PT time of 11–15 seconds and an INR of 0.8–1.2 is considered within the reference range. Your doctor will use these guidelines along with your medical history and symptoms to determine if results are normal or need further investigation.
Can diet or medications affect PT/INR results?
Yes, certain foods (like leafy greens high in vitamin K) and medications (such as warfarin, aspirin, or NSAIDs) can influence PT/INR. Always inform your doctor about all medications, supplements, or recent dietary changes that might affect blood clotting.
How often should I get a PT/INR test?
Frequency depends on your condition and treatment. People on long-term anticoagulant therapy (like warfarin) may need tests every few weeks or months to adjust medication doses. Your doctor will determine the best schedule for you.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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