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Thrombin Time (TT)

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 factor function, especially in conditions affecting coagulation.

Quick summary

["Thrombin Time helps diagnose bleeding disorders or excessive clotting risks."]

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

Key facts at a glance

LOINC
3243-3
Short code
Thrombin time
Synonyms
Thrombin 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-thrombin-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

What This Test Measures

Thrombin Time (TT) evaluates the final steps of blood clotting. When thrombin is introduced to the blood sample, it converts fibrinogen into fibrin, forming a clot. The test measures the time taken for this clotting process to occur, providing insight into the efficiency of the coagulation cascade.

Why It’s Done

Doctors may order Thrombin Time to check for bleeding disorders (e.g., hemophilia), evaluate anticoagulant medications (like heparin), or monitor conditions affecting clotting, such as liver disease or disseminated intravascular coagulation (DIC).

Sample Collection

Blood is drawn from a vein, typically in the arm, and sent to the lab. Plasma (liquid part of blood without clotting factors) is used for testing, often after centrifugation to separate it from cells.

Test Results Interpretation

Results are compared to a baseline or previous tests to identify abnormalities. Prolonged times may suggest deficiencies in clotting factors or anticoagulant effects, while shortened times could indicate hypercoagulability (e.g., from clotting disorders).

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Thrombin Time

Frequently asked questions

What does prolonged thrombin time mean?
A prolonged thrombin time may indicate impaired clotting due to missing or dysfunctional clotting factors (e.g., factor XIII deficiency), anticoagulant medications, or liver disease that affects protein synthesis. This can lead to excessive bleeding risk.
What does a normal thrombin time indicate?
A normal thrombin time suggests healthy clotting function, but it doesn’t rule out other bleeding risks. It’s often used alongside other tests (e.g., PT/INR) for a full picture.
Can food or medications affect thrombin time?
Certain medications (like heparin) or liver conditions can alter thrombin time. Avoiding certain foods (e.g., vitamin K-rich foods) or supplements may be advised before testing if your doctor recommends it.
  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