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Vitamin K-dependent clotting factor activity (Prothrombin Time, PT) with plasma

Published: August 9, 2026Updated: August 16, 2026

This test measures how long it takes for your blood to clot, which helps assess whether your blood clotting factors are functioning properly. It’s often used to monitor treatment for conditions like blood clotting disorders or anticoagulant medications.

Quick summary

This test helps doctors check if your blood is clotting normally and whether medications like warfarin are working as intended.

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

Key facts at a glance

LOINC
72507-7
Short code
VKORC1 c.1173C>T Bld/T Ql
Synonyms
VKORC1 c.1173C>T Bld/T Ql
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
molgen
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

Why This Test Is Done

Your doctor may order this test if you have symptoms of bleeding problems (like easy bruising or excessive bleeding), if you’re taking blood thinners, or if you have certain medical conditions that affect blood clotting, such as liver disease or blood clotting disorders. It can also be used to monitor long-term treatment for these conditions.

How the Test Works

A small amount of your blood (collected in a tube) is mixed with a special solution. The time it takes for a clot to form is measured and compared to a standard reference. This helps determine if your blood clotting factors are working as expected.

Sample Collection

Blood is drawn from a vein, usually in your arm, by a healthcare professional. You may feel a slight pinch, but it typically doesn’t cause significant discomfort. The blood is then sent to a lab for testing.

What to Expect Before the Test

No special preparation is usually needed, but if you’re on blood thinners, your doctor may advise you to stop them temporarily or adjust your dose before the test. Avoid eating or drinking anything (except water) for a few hours before the test if instructed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

A prolonged PT/INR result may indicate problems with blood clotting, such as deficiencies in vitamin K-dependent factors (e.g., factors II, VII, IX, X) or liver disease. A prolonged result could also suggest anticoagulant medication is too effective. A shortened result might indicate overactive clotting, though this is less common and requires further evaluation.

Short name

PT/INR (Serum/Plasma)

Frequently asked questions

What Does a High or Low Result Mean?
A higher-than-normal PT/INR result suggests your blood may clot too slowly, which could be due to a deficiency in clotting factors, liver issues, or excessive anticoagulant medication. A lower-than-normal result is less common but may indicate overactive clotting, which can be dangerous and requires medical attention.
Does This Test Require Special Dietary Restrictions?
Generally, no special diet is required, but if you’re on anticoagulant medication, your doctor may recommend avoiding certain foods high in vitamin K (e.g., leafy greens) for a few days before testing to get a more accurate result. Always follow your doctor’s instructions.
How Often Should This Test Be Done?
The frequency depends on your medical condition and treatment. For example, people on long-term anticoagulant therapy may need this test monthly or as directed by their doctor. Regular monitoring helps ensure your medication dose is appropriate and safe.
  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