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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
5284-5
Short code
PV2 Ab Titr Ser CF
Synonyms
PV2 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 Is Done

Your doctor may order a PT/INR test to check for liver disease, bleeding disorders, or to monitor blood thinners like warfarin. It’s also used before surgeries or procedures that could affect clotting.

How the Test Works

A small blood sample is taken from your arm and sent to a lab. The test measures how long it takes for your blood to clot after mixing with a standardized solution. The INR compares your result to a normal range to adjust for differences in testing equipment.

What to Expect Before the Test

No special preparation is needed, but inform your doctor about any medications (especially blood thinners) or recent illnesses that might affect results.

Possible Results & Next Steps

Results are reported as a PT time (in seconds) and INR value. High PT/INR may indicate bleeding risk or liver issues, while low values could signal clotting problems. Your doctor will discuss results and next steps based on your health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

PT/INR is critical for diagnosing clotting disorders, liver disease (e.g., cirrhosis), and monitoring anticoagulant therapy. Abnormal results may prompt further testing or adjustments to medication.

Short name

PT/INR

Frequently asked questions

What does a high PT/INR mean?
A high PT/INR suggests your blood clots more slowly than usual, which could indicate liver problems, vitamin K deficiency, or medications that thin the blood. Your doctor will evaluate this in context of your symptoms and other tests.
Can diet affect PT/INR results?
Certain foods rich in vitamin K (like leafy greens) can influence PT/INR, especially if you’re on blood thinners. Stick to your usual diet unless your doctor advises changes.
How often should I get this test?
Frequency depends on your condition. People on long-term blood thinners may need PT/INR checks monthly or as directed by their doctor. Follow-up testing is usually scheduled based on your treatment plan.
  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