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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 your blood to clot, helping assess liver function and blood clotting disorders.

Quick summary

["PT/INR helps track blood clotting risk and liver health by comparing your blood’s clotting time to a standard."]

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

Key facts at a glance

LOINC
5282-9
Short code
PV1 Ab Titr Ser CF
Synonyms
PV1 Ab Titr Ser CF
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
comp-fix
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 Matters

Your PT measures the time it takes for a small cut or injury to form a clot. The INR standardizes this result globally, linking it to your risk of bleeding or clotting. This is especially important for people with liver disease, those on blood thinners, or those with inherited clotting disorders.

How It’s Done

A small blood sample is taken from your arm. The lab mixes your blood with special chemicals to measure how long it takes to clot. The INR result is calculated from your PT and a standardized formula.

Common Uses

PT/INR is used to monitor liver function, diagnose bleeding disorders, check blood thinners (like warfarin), and evaluate inherited clotting risks. It’s also important for people with conditions like cirrhosis or hemophilia.

What to Expect

You’ll have a quick, minor prick to draw blood. The test itself takes minutes, but the full result may take a few days to arrive. No special preparation is needed unless your doctor instructs otherwise.

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 is typically between 0.8–1.2, but this can vary based on your health and medications. Your doctor will interpret results in the context of your overall health.
How often should I get this test?
Your doctor may recommend PT/INR testing based on your condition—such as monthly for people on blood thinners or less frequently for others. Follow-up schedules depend on your treatment plan.
Can I eat or drink before this test?
No special diet is needed, but avoid alcohol for 24 hours before testing, as it can affect blood clotting. If you’re on blood thinners, follow your doctor’s instructions.
  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