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Thrombin Time (Activated Clotting Time, ACT)

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

This test measures how long it takes for blood to clot after thrombin is added. It helps assess clotting function and detect bleeding disorders or abnormal clotting risks.

Quick summary

["Checks blood clotting speed with thrombin addition."]

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

Key facts at a glance

LOINC
87193-9
Short code
Guided Art Throm inf D1 W throm in cath
Synonyms
Guided Art Throm inf D1 W throm in cath
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
imaging-modality
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

What This Test Measures

The test evaluates the time required for blood plasma to form a clot when thrombin—a protein that speeds up clotting—is introduced. This reflects the efficiency of the intrinsic clotting pathway, which includes factors like fibrinogen and prothrombin.

Why It’s Ordered

Doctors may order this test to diagnose bleeding disorders (e.g., hemophilia), evaluate anticoagulant therapy effectiveness, or investigate unexplained bleeding or clotting issues.

Common Conditions Monitored

ACT is often used before procedures requiring blood clotting assessment (e.g., cardiac catheterization) or to monitor patients on anticoagulants like heparin.

Sample Collection & Preparation

Whole blood is collected in a special tube without anticoagulant and mixed with a thrombin solution. The time until clot formation is measured.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical significance: ACT is critical for identifying dysfunctions in the intrinsic clotting cascade, which can reveal bleeding risks or clotting abnormalities. It’s particularly useful in settings requiring precise coagulation control, such as cardiac interventions or patients on anticoagulants.

Short name

ACT (Thrombin Time)

Frequently asked questions

Why might my doctor ask for this test?
Your doctor may recommend it to check for bleeding disorders, assess anticoagulant treatment, or prepare you for a procedure that requires careful blood clotting monitoring.
What does a prolonged ACT indicate?
A longer-than-normal ACT may suggest impaired clotting (e.g., due to hemophilia, liver disease, or low fibrinogen), while a shorter ACT could indicate overactive clotting or technical issues.
How soon will I get results?
Results are typically available within 15–30 minutes, depending on lab processing, though your doctor will discuss them with you.
  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