Overview
The thrombin time (TT) is not routinely performed as part of a coagulation screen.
Normal Range
- <24 seconds
Important Lab Points
- Performed by adding thrombin to a plasma sample.
- Tests only the final step of fibrin clot formation.
- If the TT is prolonged, a reptilase test is also performed to distinguish between causes.
Diluted thrombin time may have a role in the monitoring of factor IIa inhibitors (e.g. dabigatran).
Prolonged Thrombin Time
Interpretation
- Prolonged reptilase - fibrinogen defects, fibrin degradation products
- Normal reptilase - heparin, factor IIa inhibitors
Causes of Prolonged Thrombin Time
- Fibrinogen defects - hypofibrinogenaemia, afibrogenaemia, dysfibrinogenaemia
- Fibrin degradation products (e.g. in DIC)
- Factor IIa inhibitors (e.g. dabigatran)
- Heparin
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