EXTEM

EXTEM is a ROTEM (rotational thromboelastometry) assay used to evaluate the extrinsic pathway of coagulation. In EXTEM, tissue factor is added to the blood sample to activate coagulation, and the developing clot is measured over time by changes in viscoelastic properties. The test provides a dynamic picture of clot formation and stability that complements standard coagulation tests.

Key parameters reported by EXTEM include clotting time (CT), which reflects the initiation phase; clot formation time (CFT), representing the speed of clot development; and maximum clot firmness (MCF), indicating the overall strength of the clot. Additional commonly used metrics include the alpha angle and amplitudes at fixed times (such as A5 or A10). Some systems also report lysis-related indices to assess fibrinolysis. In general, EXTEM emphasizes contributions from the tissue factor-activated coagulation cascade and the platelets to clot strength.

Clinical use of EXTEM spans trauma, major surgery, obstetrics, and liver disease, where rapid assessment of coagulopathy is crucial. It helps identify whether bleeding risk stems from factor deficiencies, platelet dysfunction, or fibrinogen depletion, and it supports decisions on transfusion and targeted therapies such as fibrinogen supplementation, platelets, plasma, or antifibrinolytics. EXTEM is often interpreted alongside INTEM (intrinsic pathway) and FIBTEM (fibrin-based clot strength) to differentiate etiologies of coagulopathy. Limitations include sensitivity to anticoagulants like heparin, which may be accounted for with additional assays.