Thrombin clotting time (TCT) measures the time for a fibrin clot to form after thrombin is added directly to a plasma sample, bypassing the earlier steps of the coagulation cascade. It specifically measures the final step of coagulation — thrombin's conversion of fibrinogen to fibrin.
TCT is prolonged when fibrinogen is low (hypofibrinogenaemia), abnormal (dysfibrinogenaemia), when thrombin inhibitors such as heparin or dabigatran are present in the sample, or when fibrin degradation products (from conditions like DIC) inhibit fibrin polymerisation. TCT is most commonly used to detect heparin contamination in blood samples and to investigate abnormal bleeding alongside PT and APTT.
FAQs
Why is TCT sensitive to heparin?
Even trace heparin prolongs TCT dramatically, making it the best test for detecting unsuspected heparin contamination.
What is the reptilase time?
Reptilase converts fibrinogen to fibrin but is not inhibited by heparin. If TCT is prolonged but reptilase is normal, heparin is the cause. If both are prolonged, the problem is with fibrinogen.
Is TCT used to monitor dabigatran?
TCT confirms dabigatran presence. Dilute TCT or anti-thrombin assays are preferred for quantitative assessment.
What is dysfibrinogenaemia?
Structurally abnormal fibrinogen that does not polymerise normally, causing prolonged TCT and reptilase time despite normal fibrinogen quantity. It can be inherited or acquired from liver disease.
