Clotting time dependence

Prothrombin time PT is performed by adding thromboplastin (tissue) factor and calcium to citrate-anticoagulated plasma, recalcifying the plasma, and measuring the clotting time. The major utility of PT is to measure the activity of the vitamin K-dependent factors II, VII, and X. The PT is used in evaluation of liver disease, to monitor warfarin anticoagulant effect, and to assess vitamin K deficiency. 

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. 

The steady flow rate observed in the heparin infusion study with the corresponding delay in clotting time indicates that the infusion device can provide dependable controlled release. Since the service life, size and flow rate of the device may be varied depending on the requirements of an experiment, these features should make it readily adaptable to the infusion of many other drugs. 

The general drawback of the Wessler model is the static nature of the venous thrombus development. To overcome this problem some investigators have developed more dynamic models with reperfusion of the occluded vessel segments after clot development. Depending on the time of test compound administration (pre- or post-thrombus initiation), the effect on thrombus growth and fibrinolysis can be evaluated. Levi et al. (1992) have used this model to assess the effects of a murine monoclonal anti-human PAI-1 antibody and Biemond et al. (1996) compared the effect of thrombin and factor Xa inhibitors with a low molecular weight heparin. 

Superwarfarins lower the blood concentrations of the vitamin K-dependent clotting factors II, VII, IX and X this results in prolongation of prothrombin time (PT) and partial thromboplastin time (PTT). PT and PTT should be repeated at least twice daily until a normal PT and PTT are established. Also, the blood clotting time and the bleeding time should be measured. Blood is often demonstrable in the excreta. Secondary hypochromic or microcytic anemia may be marked (Goldfrank et al, 2002 Nelson et al, 2006). 

The prothrombin time (PT), as proposed by Quick, is the most commonly performed coagulation function test. It is used to monitor oral anticoagulant therapy and also as a preoperative screening test to warn of possible bleeding risk in patients with a personal or family history of bleeding (Table 36-2). Measured clotting times are extremely dependent on the animal and tissue source and the quality of the thromboplastin used. Variability can be expected because of the assay s dependence on the number of tissue factor molecules and the quantity of... 

When heparin is administered intravenously, the material disappears from the blood very rapidly . The relation between blood levels, rate of disappearance of heparin from the circulation and urinary excretion indicate one of the valuable pharmacological properties of heparin. It is cumulative only at low blood concentrations. At blood concentrations which give measurable clotting times, the rate of removal is dependent on the concentra-... 

Other tests used, which in some instances offer more sensitivity to specific aspects of therapy, include the prothrombin-proconvertin ratio (PP), the thrombotest, the liirombin clotting time test (TCT, activated clotting time, aetivated eoagulation time), the platelet count and the bleeding time test. The use of the most appropriate test will depend on the situation and the desired result. 

Thrombin clotting time 70 to 120 seconds 1 50 to 600 seconds depending on indication for anticoagulation... 

For metabolomic analysis of blood, both serum and plasma samples are used. With respect to serum samples, details such as clotting time, clotting temperature, and treatment conditions prior to centrifugation need to be considered (Teahan et al. 2006). For collection of plasma samples it is important to consider the anticoagulant to be used and the possibility of unwanted peaks (Scalbert et al. 2009). It should be noted that the choice of anticoagulant will depend on the method employed downstream and the metabolites to be analysed. For NMR-based metabolomics, lithium heparin plasma is most suitable whereas for studying lysophospholipids EDTA plasma is recommended (Seppanen-Laak-so and Oresic 2009). 

Biological characterization of the cellulose-heparin fibers performed by measuring the clotting kinetics of human whole blood exposed to these fibers using thromboelas-tography showed cellulose/heparin composite fibers afford a prolonged clotting time in a concentration-dependent fashion. The observed results indicates that presence of... 

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