Thrombin clotting time

The Thrombin Clotting Time (TCT), also known as the Thrombin Time (TT), is a coagulation assay which is usually performed in order to detect for the therapeutic level of the anticoagulant Heparin. It is also sensitive in detecting the presence of a fibrinogen abnormality.


Within the realm of coagulation assays, the Thrombin Clotting Time is one of the most procedurally simple. After liberating the plasma from the whole blood by centrifugation, bovine Thrombin is added to the sample of plasma. The clot is formed and is detected optically or mechanically by a coagulation instrument. The time between the addition of the thrombin and the clot formation is recorded as the thrombin clotting time

Specimen Requirements

Whole blood is taken with either citrate or oxalate additive (if using the vacutainer system, this is a light blue top tube). As with other coagulation assays, the tube must not be over- or under-filled in order to ensure the correct anticoagulant-to-blood ratio: 1 part anticoagulant per 9 parts blood.

Reference Interval

The reference interval of the Thrombin Clotting time is generally <21 seconds, depending on the method and the endemic patient population. Results outside of reference interval indicate heparin therapy, Hypofibrinogenemia, hyperfibrinogenemia fibrinogen abnormality, or Lupus anticoagulant.

Causes for specimen rejection

Causes for Rejection of the specimen include QNS, severe hemolysis, improper storage or delay in processing, error in labeling.


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