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Prothrombin Time (PT)

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

This test measures how long it takes for blood to clot after the addition of a specific reagent. It helps assess the function of blood clotting factors, particularly those involved in the extrinsic pathway.

Quick summary

["PT helps doctors check if your blood clotting process is working as it should."]

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

Key facts at a glance

LOINC
5902-2
Short code
Prothrombin time
Synonyms
Prothrombin time
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
coag-tissue-factor-induced
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

PT is commonly used to monitor treatment with blood-thinning medications like warfarin. It also helps diagnose bleeding disorders or clotting issues, especially when other clotting factors may be affected.

What to Expect During the Test

A small amount of blood is drawn from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The test itself is quick and painless.

How the Results Are Used

Your PT result is compared to a standard range to determine if your blood clotting is normal or if it’s slower or faster than expected. This helps guide treatment decisions.

Common Reasons for Testing

Doctors may order a PT test if you’re on blood thinners, have liver disease (which affects clotting factors), or are suspected of having bleeding disorders like hemophilia.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

PT

Frequently asked questions

What does a normal PT result mean for me?
A normal PT result suggests your blood clotting process is functioning within expected limits, but it doesn’t rule out all clotting or bleeding issues. Your doctor may still recommend further testing if needed.
Can I eat or drink anything before this test?
You can eat and drink normally before the test unless your doctor specifies otherwise. Some tests may require fasting, but PT does not.
How long will I need to wait for my results?
Results are typically available within a few hours to a couple of days, depending on your lab. Your doctor will discuss them with you during your follow-up visit.
  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