thrombintime

Thrombin time, occasionally written as thrombintime, is a laboratory assay that measures the time required for plasma to clot after the addition of a standardized amount of thrombin in the presence of calcium. The test specifically assesses the conversion of fibrinogen to fibrin and is influenced by the functional level of fibrinogen as well as by inhibitors of thrombin.

In practice, citrated plasma is incubated with a defined thrombin reagent and calcium, and the time to visible clot formation is recorded. Normal values vary by reagent and instrument but are typically in the range of about 14 to 20 seconds. Prolongation can indicate hypofibrinogenemia or dysfibrinogenemia, as well as the presence of inhibitors or interfering substances.

Thrombin time is particularly sensitive to the presence of heparin and to direct thrombin inhibitors (such as dabigatran). It can therefore be used to detect residual heparin in a sample or to screen for the effect of thrombin-targeting anticoagulants, though it is not the main test for routine anticoagulation monitoring. Reagents and methods differ between laboratories, and results should be interpreted with reference to the specific assay used.

Interferences include sample quality issues (hemolysis, lipemia, icterus), improper sample handling, and concurrent abnormalities in fibrinogen or other coagulation factors. A reptilase time can be used alongside thrombin time to help distinguish fibrinogen abnormalities from thrombin inhibitors, since reptilase time is less affected by heparin and direct thrombin inhibitors.