Activated clotting time measurement

The main cause of debate at present with regard to UFH centers on the amount used peri-PCI. The level of anticoagulation produced by UFH is measured by the activated partial thromboplastin time and activated clotting time (ACT), the latter being available in the cardiac catheter laboratory as a near-patient test. 

Determination of the potency of Factor VIII is also difficult. This is normally measured by the abiUty of the sample to correct the clotting time of plasma deficient in Factor VIII. A number of methods and practices have evolved for this purpose (231), but these give very different results, particularly when activation of products may also occur (232). International standards have been used, but further standardization of the analytical method and harmonization of working standards is underway (233,234) under the auspices of the ISTH and the EC. 

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. 

The anticoagulant activity of dextran derivatives were assessed by measuring the thrombin clotting time (ThNIH units) of freshly prepared platelets from plasma in the presence of the CMD, CMDB, CMDBSSu and CMDSu polymers and of human thrombin (1094 NIH units mL 1). The anticomplementary activity was expressed as the amount of polymer that inhibits 50% formation of the alternative and classical pathway C3 convertase [220,290,291]. 

For in-hospital patients receiving heparin, a blood sample is drawn, at least daily. The red cells are centrifuged from the sample leaving only plasma. An agent that activates the clotting cascade is added to a fixed amount of plasma. The time required for a clot to form, called the clotting time, is then measured. In addition to the patient s plasma, normal plasma is also tested. 

The term coagulation factor deficiency is frequently ambiguous. Previously, it implied a deficit in the functional activity of a component because the clotting time tests measured only the ability of the component to support normal coagulation. The reference for normal functionality is the response of dilutions of plasma from pooled... 

Figure 8. In vitro heparin removal from citrated rabbit blood by passing heparin through a 500-1xL Sepharose-heparinase column at a flow rate of 0.5 mL/min. The anticoagulant activity as measured bu both Factor Xa and whole blood clotting time is shown for the untreated blood and for the blood cycled through either the natured or denatured Sepharose-heparinase...

We now report results concerning the interactions between these two proteins and two of these polystyrene derivatives sulfonated polystyrene (PSSO3) and sulfonate-glutamic acid sulfonamide polystyrene (PSSO2GIU). The adsorption of each protein was studied either in purified system or in plasma and the binding constants were determined. Moreover, the catalysed formation of thrombin-anti-thrombin III complex was examined and compared with the antithrombic activity measured through thrombin clotting times of plasma preincubated with these polymers. 

The classical method for the biological testing of vitamin K-active substances is the measuring of their effect on the blood clotting time of the vitamin K-deficient chick. Dam et al. (1951) have described a modified method, by which a linear relationship between vitamin K dosage and clotting time was obtained. 

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