Thrombin Time

Purpose

• Screening test for hypofibrinogenemia, hyperfibrinogenemia, abnormalities of the fibrinogen molecule, and inhibitors agains thrombin or fibrin.
• Tests the conversion of fibrinogen to fibrin to cross-linked fibrin.
• Monitor anticoagulant therapy with fibrinolytic agents and hirudin..
• When modified (using high concentration of thrombin), the test can be used to measure fibringoen levels.

• Collect blood from the patient into a citrated tube
• Take the collected blood to the laboratory
• Centrifuge to isolate the plasma
• Take small sample of the plasma ~0.1 ml.
• Add bovine thrombin to plasma
• The time that elapses until clot forms is the Thrombin Time (TT).

• TT shorter than the reference range is  not associated with any clinical condition is usually related to improper procedure.
• Prolongation of the TT occurs when there is:

1. Contamination with heparin.  TT can be repeated after addition of protamine sulfate and will be normal..
2. Afibrinogenemia/Hypofibrinogenemia - acquired (DIC, liver disease) and familial
3. Interference with fibrinopeptide cleavage