Thrombin Time

The Thrombin Time (TT) is the time taken for a plasma sample to clot on addition of thrombin. The test is essentially a measure of fibrinogen to fibrin conversion and the factors affecting this terminal stage of the coagulation system.

The TT will be prolonged by the following:

1. Presence of heparin
2. Low (<80 mg/ml) fibrinogen levels
3. Presence of an abnormal fibrinogen (dysfibrinogenemia)
4. Presence of fibrin split products
5. Presence of a Direct Thrombin Inhibitor (DTI) drug (e.g. lepirudin, argatroban or bivalirudin)

The interpretation of a prolonged TT is greatly aided by the parallel performance of a Reptilase Time. This test is insensitive to heparin (the most common cause of a prolonged TT) and DTIs. Thus, a very prolonged TT with a normal RT is indicative of the presence of one of these anticoagulant agents. Heparin can be removed by Hepzyme treatment of the plasma sample. There is no way to remove or neutralize a DTI at the present time.

The RT is equally sensitive to low fibrinogen levels and is often more prolonged than the TT in the presence of a dysfibrinogenemia

In the Hemostasis and Thrombosis Laboratory, the normal range for the Thrombin Time is 18.5 - 26.9 seconds.