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

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 affecting blood clotting and guide treatment decisions."]

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

Key facts at a glance

LOINC
46417-2
Short code
PT BldC
Synonyms
PT BldC
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
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
coag-tissue-factor-induced
CPT
85610
SNOMED
396252006
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What Does PT/INR Measure?

PT measures the time it takes for a clot to form in your blood when mixed with specific reagents. INR standardizes these results globally by comparing them to a reference sample, ensuring consistency across labs. This test evaluates the activity of clotting factors produced by the liver, which rely on vitamin K for proper function.

Why Might Your Doctor Order This Test?

Your doctor may order PT/INR to check for bleeding disorders, monitor blood thinners (like warfarin), diagnose liver disease, or evaluate conditions affecting clotting, such as vitamin K deficiency or blood clots.

Common Conditions Monitored with PT/INR

PT/INR is frequently used to track patients on anticoagulant medications to prevent excessive clotting or bleeding. It’s also important for those with liver disease, since the liver produces clotting factors.

How Is the Test Performed?

A small blood sample is taken from a vein, usually in your arm. The blood is mixed with special reagents to measure clot formation time. The INR result is calculated based on your PT and a standardized reference.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: whole-blood

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 Are Normal Results?
Normal results vary slightly by lab, but a PT is typically around 11–13 seconds, and an INR is usually between 0.8 and 1.2. Higher INR values (above 1.2) may indicate bleeding risk, while lower values (below 0.8) could suggest clotting issues. Your doctor will interpret results in the context of your health and treatment plan.
How Often Should I Get This Test?
Frequency depends on your condition and treatment. If you’re on blood thinners, your doctor may order PT/INR tests weekly, monthly, or as needed to adjust your medication.
Can I Eat or Drink Before the Test?
You can eat and drink normally before the test unless your doctor specifies otherwise. Avoid alcohol or certain medications that may affect clotting for 24 hours before testing.
  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