TEM investigates the interaction of coagulation factors, their inhibitors, anticoagulant drugs, blood cells, specifically platelets, during clotting and subsequent fibrinolysis.
They allow testing in the presence of therapeutic heparin concentrations and provide differential diagnostic information to support decisions in therapy.
TEM detects both hypo- and hyperfunctional stages of the clotting process and is probably the only reliable rapid test for the diagnosis of hyperfibrinolysis.
The rapid availability of results helps to discriminate surgical bleeding from a true haemostasis disorder and improves the therapy with blood products, factor concentrates, anticoagulants and protamine, hemostyptic and antifibrinolytic drugs.
A disposable pin is attached to a shaft which is connected with a thin spring (the equivalent to Hartert’s torsion wire in thrombelastography) and slowly oscillates back and forth.
[7] In contrast to thrombelastography with its pendulum-like principle, the design of the TEM viscoelastic detection system (figure 1) makes it quite robust and insensitive against mechanical shocks or vibrations.
[citation needed] The primary result of TEM is a reaction curve which shows the elasticity over time when the clot forms or dissolves.
These parameters denote the speed at which a solid clot forms and are primarily influenced by platelet function, but to a certain extent especially fibrinogen and coagulation factors contribute.
[11] Higher concentrations of heparin can also prolong CFT in the INTEM assay, but not in HEPTEM, EXTEM, FIBTEM or APTEM (see under “reagents”).
The ML parameter describes the percentage of lost clot stability (relative to MCF, in %) viewed at any selected time point or when the test has been stopped.
While in normal blood fibrinolysis activity is quite low, in clinical samples a more rapid loss of clot stability by hyperfibrinolysis may lead to bleeding complications which can be treated by the administration of antifibrinolytic drugs.
In the case of monocausal haemostasis disorders, the resulting reaction curves may be quite typical; however, under most clinical conditions this approach has severe limitations.
Absence of a controlled activation step leads to inferior reproducibility and very long test times which are not acceptable for POC applications.
[12][13][14] Application of this strategy helps to minimize the exposure of patients to allogeneic blood products which have certain risks; and it saves costs.
FIBTEM results correlate well in many cases with the Clauss fibrinogen assay, but is additionally influenced by fibrin polymerization disorders which cannot reliably be detected with clotting tests.
TEM-guided transfusion of blood products or factor concentrates in cardiac, hepatic and major orthopedic surgery is the main application of the method.
Moreover, it is successfully used in the complex situation of (poly)trauma, or in decision making for of alternative therapy such as antifibrinolytic drug administration .
The sensitivity for coagulation factor deficiencies, including those induced by oral anticoagulation, is less pronounced as compared to clotting assays.
However, due to the rapid availability of differential diagnostic information, TEM has become an established method in surgical procedures where blood losses can be expected.