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Prothrombin Activity (Serum/Plasma)

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

This test measures how well your blood can clot, focusing on prothrombin—a protein essential for blood clotting. It helps assess bleeding disorders or liver function.

Quick summary

["Evaluates blood clotting efficiency and liver health."]

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

Key facts at a glance

LOINC
40457-4
Short code
Prothrom Ab SerPl-aCnc
Synonyms
Prothrom Ab 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
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 doctor may order this test if you have symptoms like easy bruising, excessive bleeding, or if they suspect liver disease, blood clotting disorders, or conditions affecting vitamin K levels.

Common Reasons for Testing

Tests are often done before surgeries, during treatments for blood disorders, or to monitor conditions like liver disease or anticoagulant medications.

Sample Collection and Preparation

Blood is drawn from a vein, typically in the arm. The sample is collected in a tube that separates serum or plasma from blood cells. This test does not require fasting.

Test Process and Results

The test measures the time it takes for blood to clot under controlled conditions. Results are often reported as a percentage or ratio compared to a standard reference.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

PT Activity

Frequently asked questions

What does a low result mean?
A lower-than-normal result may indicate problems with blood clotting, liver disease, or deficiencies in vitamin K. It can also signal conditions like hemophilia or other coagulation disorders.
What does a high result mean?
High results are less common but may suggest rare clotting disorders or specific medications affecting clotting factors.
How often should I get this test?
Frequency depends on your health condition and treatment plan. Your doctor will determine how often this test is needed based on your medical history and symptoms.
  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