Thrombin time

Purified thrombin is added to plasma samples and the time for clotting is measured. This test, the thrombin time (TT), primarily reflects the concentration of fibrinogen. However, it also reflects the ability of the fibrinopeptides to be cleaved and the polymerization of fibrinogen. Separation of these three contributions requires a quantitative measurement of the concentration of fibrinogen that is not related to time for clot formation. The thrombin time can be prolonged if heparin is present in the patient s plasma sample because it will promote preferential inactivation of the added thrombin by antithrombin and reduce the amount of thrombin that can act on fibrinogen. 

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A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

V Mucosal tract bleeding Prolonged PT and aPTT Normal thrombin time Specific factor V assay... 

XIII Umbilical cord, intracranial, and joint bleeding recurrent miscarriages, impaired wound healing Normal PT, aPTT, thrombin time, bleeding time Specific factor XIII assay... 

In a patient presenting with a bleeding or clotting disorder, an initial evaluation should include bleeding time, prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time, and platelet count. 

Thrombin time is an assessment of the time required for the appearance of the fibrin clot after thrombin is added... 

Acute pulmonary emboli IV Infusion 100 mg over 2 hr. Institute or reinstitute heparin near end or immediately after infusion when aPTT or thrombin time (TT) returns to twice normal or less. 

E. Therapeutic response Intravenous bivalirudin produces a rapid and dose-dependent prolongation of the activated partial thromboplastin time (aPTT), prothrombin time, activated clotting time (ACT), and thrombin time. 

Substances Thrombin time of oxalate filled plasma, (s) The lysis time (h) at 37 °C of a clot produced from ... 

Heparin content, °/ /o Thrombin time, min Recalcification time, min... 

Determined as follows 1 mg of the copolymer was dispersed in a 0.1 ml solution of non-ionogenic surface-active compound at 37 °C for 10 min 0.2 ml of plasma were added to the suspension the mixture was incubated for 15 min at 37 °C 0.1 ml thrombin (5 U/ml) (thrombin time) or 0.2 ml of 0.025 M CaCl2 (recalcification time) were then added and the time of clot formation was measured. 

The sorbed heparin fully retains its anticoagulant activity the thrombin time for both sorbed heparin and heparin in solution is 20 + 2 s/mg heparin. The clotting time of blood in contact with the gel is proportional to the amount of heparin sorbed and significantly higher than that characteristic for the non-heparinized gel. Heparin may be repeatedly sorbed after it has been removed with saturated NaCl solution. 

Thrombin Time (TT). To 0.1 ml of citrated plasma 0.1 ml of diethylbarbiturate-citrate buffer, pH 7.6 (Behring Werke, Marburg) is added and the mixture is incubated for 1 min at 37 °C. Then 0.1 ml of bovine test-thrombin (30 IU/ml, Behring Werke, Marburg) is added and the coagulometer is started. The time to clot formation is determined. The TT measures effects on fibrin formation. 

Protein C and S, antithrombin III, activated protein C resistance, thrombin time ... 

Each of these tests is also affected by the final common pathway, the endpoint of which is tested by the thrombin time. This tests the formation of a fibrin clot by the addition of exogenous thrombin and calcium. It is sensitive to the level of endogenous fibrinogen and to the presence of inhibitors of thrombin (heparin, PDFs). 

Etherified starch shortens the thrombin time by a fibrinoplastic effect. This accelerates the conversion of fibrinogen to fibrin, resulting in a less stable thrombus, which is more susceptible to lysis. The macromolecules in etherified starch induce an acquired von Willebrand s syndrome with reduced concentrations of aU three main forms of factor VIII factor VIILC, von WiUebrand factor, and von WiUebrand factor antigen (vWFag). 

In three patients who underwent cardiovascular surgery subsequent abnormalities in hemostasis, characterized by increased activated partial thromboplastin time, prothrombin time, and bovine thrombin time, and by a markedly reduced concentration of factor V, developed between the seventh and eighth postoperative days after exposure to fibrin glue containing bovine thrombin (13). It was suggested that the glue also contains small amounts of factor V and that this may have caused the abnormalities. 

Galanakis DK, Newman J, Summers D. Circulating thrombin time anticoagulant in a procainamide-induced syndrome. JAMA 1978 239(18) 1873-4. 

As well as reducing platelet count or function valproate can impair procoagulatory thrombocytic functions as reflected by reduced platelet activation and an increased thrombin time (56). Valproate-induced platelet... 

In human medicine, starches with smaller average molecular weights have less profound effects on hemostasis (Treib et al 1999). This may also be the case in horses, although only one dose has been tested. In healthy horses, a 8ml/kg dose of a 10% pentastarch solution resulted in a slight decrease in the thrombin time 12 h after administration, which returned to normal after 24 h. No effect on prothrombin time or partial thromboplastin time was documented (Meister et al 1992). In healthy horses, the initial phase half-life of pentastarch is 5.6 h and the terminal phase half-life is 122 h. However, the effects on PCV, plasma total solids and plasma viscosity appear to last only 12-24 h (Meister et al 1992). In equine clinical cases, the half-life may be as short as 2h (Hermann et al 1990). Pentastarch, although available in the USA, is only approved for leukapheresis in human medicine. 

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