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

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

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

Quick summary

["PT/INR checks liver health and blood clotting risk—critical for monitoring conditions like liver disease or blood thinners."]

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

Key facts at a glance

LOINC
24172-9
Short code
PV2 NAb sp2 Titr Ser Nt
Synonyms
PV2 NAb sp2 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

What Is PT/INR Used For?

PT/INR evaluates your blood’s ability to clot and helps diagnose or monitor conditions like liver disease, bleeding disorders, or medications that affect clotting (e.g., warfarin). It also ensures safe dosing of anticoagulants.

How Is the Test Performed?

A small blood sample is drawn from a vein. The test measures how long it takes for clotting to occur, with results expressed as PT (in seconds) and INR (a standardized ratio).

Why Might You Need This Test?

You may need PT/INR if you have liver disease, a bleeding disorder, or are taking blood thinners like warfarin. Doctors also use it to check if medications are working properly.

What Do Results Mean?

PT/INR results compare your clotting time to a standard. Higher INR values (above 1.5) may indicate bleeding risk, while lower values (below 1.2) could signal clotting issues. Your doctor will interpret results based on your medical needs.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: PT/INR is essential for diagnosing liver dysfunction (e.g., cirrhosis), detecting clotting disorders, and monitoring anticoagulant therapy. Abnormal results may prompt further testing or adjustments to treatment.

Short name

PT/INR

Frequently asked questions

Why do doctors order PT/INR tests?
Doctors order PT/INR to check liver function, detect bleeding risks, or ensure blood thinners are working correctly—especially in patients with conditions like liver disease or those on anticoagulants.
What happens if my PT/INR is too high or too low?
High PT/INR (e.g., INR >2.0) may mean you’re at risk of bleeding, while low PT/INR could indicate clotting problems. Your doctor will discuss next steps, such as adjusting medications or further testing.
Can diet or medications affect PT/INR results?
Yes—vitamin K, certain medications (e.g., warfarin), and foods high in vitamin K (leafy greens) can influence PT/INR. Always inform your doctor about all medications or supplements you take.
  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