Thrombin time

An article about the thrombin time test in coagulation studies

Diagram of the coagulation cascade in vivo

The thrombin time (TT) is a blood test that measures the time it takes for a clot to form in the plasma of a blood sample after an excess of thrombin has been added. This test is used to assess the final step of the coagulation process, which is the conversion of fibrinogen to fibrin.

Purpose

The thrombin time is primarily used to evaluate the presence of fibrinogen abnormalities, either quantitative or qualitative, and to detect the presence of inhibitors that affect the conversion of fibrinogen to fibrin. It is particularly useful in diagnosing dysfibrinogenemia, hypofibrinogenemia, and the presence of heparin or other direct thrombin inhibitors in the blood.

Procedure

In the thrombin time test, a sample of the patient's plasma is mixed with a standardized amount of thrombin. The time taken for a clot to form is measured in seconds. The normal range for thrombin time is typically between 14 to 19 seconds, but this can vary depending on the laboratory and the specific reagents used.

Clinical Significance

A prolonged thrombin time can indicate several conditions:

• Hypofibrinogenemia or afibrinogenemia: Low levels of fibrinogen in the blood.
• Dysfibrinogenemia: Abnormal fibrinogen molecules that do not function properly.
• Heparin therapy: The presence of heparin, an anticoagulant, can prolong thrombin time.
• Direct thrombin inhibitors: Medications such as dabigatran can also prolong thrombin time.

Interpretation

The thrombin time is often used in conjunction with other coagulation tests such as the prothrombin time (PT) and the activated partial thromboplastin time (aPTT) to provide a comprehensive assessment of the coagulation system. A normal thrombin time with prolonged PT and aPTT may suggest a specific inhibitor or factor deficiency.

Limitations

The thrombin time is sensitive to the presence of heparin and other direct thrombin inhibitors, which can lead to falsely prolonged results. Therefore, it is important to consider the patient's medication history when interpreting the results.

Related pages

• Coagulation
• Fibrinogen
• Thrombin
• Prothrombin time
• Activated partial thromboplastin time