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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 blood to clot, helping assess blood clotting function and identify bleeding or clotting disorders.

Quick summary

["Helps doctors check if blood clotting is working as it should."]

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

Key facts at a glance

LOINC
40824-5
Short code
vWF Cp Inhib PPP-aCnc
Synonyms
vWF Cp Inhib PPP-aCnc
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
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

What Does This Test Measure?

The test evaluates the time it takes for a small cut or injury to form a stable blood clot. The INR standardizes results across different labs by comparing your PT to a normal reference range. This helps diagnose conditions like bleeding disorders, liver disease, or blood thinners (anticoagulants) in use.

Why Might You Need This Test?

Your doctor may order this test if you have symptoms like excessive bleeding, easy bruising, or if you’re taking medications that affect blood clotting (e.g., warfarin). It’s also used to monitor long-term treatment for conditions like atrial fibrillation or after liver surgery.

How Is the Test Done?

A small blood sample is drawn from a vein, usually in your arm. The blood is mixed with a special solution to measure clotting time. The INR is calculated based on your PT result compared to a standard.

What Are Common Results?

Results are reported as a PT time (in seconds) and INR value. While exact ranges vary by lab, an INR of 1.0 is typical for healthy individuals. Higher or lower values may indicate abnormal clotting function.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance:

Short name

PT/INR

Frequently asked questions

Why is this test important for my health?
This test is critical for managing conditions that affect blood clotting. For example, an elevated INR may signal bleeding risks, while a prolonged PT could indicate liver disease or deficiencies in clotting factors. Regular monitoring helps prevent complications from medications like warfarin, ensuring safe dosing.
What does an abnormal result mean?
An abnormal result may mean your blood clots too slowly (increased risk of bleeding) or too quickly (increased risk of clots). Your doctor will discuss findings with you and may recommend lifestyle changes, medication adjustments, or further testing based on your symptoms and medical history.
How often should I get this test?
Your doctor will determine how often you need this test based on your health condition and treatment plan. For example, people on long-term anticoagulant therapy may need regular INR checks, while others may only need it occasionally.
  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