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

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 potential bleeding or clotting disorders.

Quick summary

["PT/INR checks your blood’s ability to clot safely."]

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

Key facts at a glance

LOINC
40596-9
Short code
Prothrom IgM SerPl-aCnc
Synonyms
Prothrom IgM SerPl-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 This Test Measures

Prothrombin Time (PT) evaluates the time it takes for blood to clot after the start of the clotting process. The INR standardizes this measurement globally, providing a consistent way to compare results across labs. Together, they help doctors monitor conditions like liver disease, blood clotting disorders, or medications like warfarin.

Why It’s Done

Your doctor may order a PT/INR test if you have symptoms like easy bruising, excessive bleeding, or if you’re taking blood thinners. It’s also used to monitor long-term treatment for conditions affecting blood clotting.

Sample Collection

A small blood sample is drawn from a vein, usually in your arm. The blood is processed to separate serum (the liquid part without clots), which is then tested for clotting time.

Common Conditions

Abnormal results may indicate issues like vitamin K deficiency, liver disease, or inherited clotting disorders. High PT/INR could mean increased bleeding risk, while low values might suggest over-clotting or medication side effects.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

PT/INR

Frequently asked questions

How long does it take to get results?
Results are typically available within 24 hours, depending on lab processing times. Follow-up with your healthcare provider for interpretation.
Can I eat or drink before this test?
No special diet is needed, but avoid blood-thinning foods like leafy greens (high in vitamin K) 24 hours before testing if on certain medications.
What does a high or low PT/INR mean?
A high PT/INR suggests increased bleeding risk, while a low value may indicate over-clotting or medication effects. Your doctor will discuss results in context with your medical history.
  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