Blood Clotting Test

The concept that different structural domains on the heparin chains are principally involved for optimal activity in the foregoing interactions could not be perceived in early work on structure-activity correlations, because the activity of heparin has been most frequently evaluated only with whole-blood-clotting tests (such as the U.S.P. assay). Development of assays for specific clotting-factors (especially Factor Xa and thrombin) has permitted a better insight into the mechanism of action of heparin at different levels of the coagulation cascade. 

Blood-clotting tests. Since the liver synthesises many of the blood-clotting proteins, bloodclotting tests may be used as a marker of the severity of certain liver disorders. 

Blood clotting tests revealed that thrombus formation on the PBLG, PBDLG, PZLL and polysarcosine-based PDMS triblock copolymer films was reduced in comparison to glass surfaces and the respective homopolymers [67]. A systematic variation of block copolymer chain length and composition... 

In vitro biocompatibility tests were also performed by Neenan et al. (1982). They used heparinized poly[(organo)phosphazenes] to enhance the anti-thrombogenic properties of polyphosphazenes. Films of these materials containing heparine were subjected to bovine blood clotting tests (Figure 29). 

Any material implanted in the bloodstream will be coated with protein almost instantaneously. Typically, in preparation for a second implantation, formaldehyde solution is used for disinfectant purposes after removing the unit from the first animal. The formaldehyde treatment apparently plays an important part in the improved results achieved during second and subsequent implants. To confirm this experience, a similar type of experiment has been performed with our in vitro model. Silastic samples were exposed to dog blood for 3 hours at room temperature and then afterward one surface was treated with 4% formaldehyde and soaked in distilled water. The other sample was untreated. A new surface and the untreated used surface did not show significant differences in the subsequent blood clotting test, but the surface treated with formaldehyde showed improved thrombo-resistaiihe. 

Duplex ultrasonography is the most commonly used test to diagnosis DVT. It is a non-invasive test that can measure the rate and direction of blood flow and visualize clot formation in proximal veins of the legs. It cannot reliably detect small blood clots in distal veins. Coupled with a careful clinical assessment, it can rule in or out (include or exclude) the diagnosis in the majority of cases. 

Prothrombin time (PT) A measure of coagulation representing the amount of time required to form a blood clot after the addition of thromboplastin to the blood sample PT is also known as Quick s test. 

Blood access devices, 3 719-720 Blood alcohol tests, 12 96 Blood clots, 4 82-83 Blood clotting, vitamin K in, 25 795 Blood coagulation, 4 84-90... 

The fact that thromboresistance of HCP is dependent on the method of immobilization of heparin, together with a rather low activity of covalently immobilized heparin, makes the idea of long-term enhancement of thromboresistance of polymers on their heparinization doubtful 54,70,71J. Naturally, the answer can be given only after a detailed analysis of the interaction of HCP with blood and its components and clarification of the mechanism of the effect of the immobilized heparin on the blood clotting system and relying on the results of in vivo tests of these materials are necessary. 

More extensive studies were carried out on polymeric materials modified with a hydrogel containing covalently immobilized heparin and trypsin 136,137>. Table 18 compiles the results of in vitro tests of the thus-modified low-density polyethylene. Obviously, co-immobilization of heparin and proteolytic enzyme onto polyethylene results in an increase of the blood clotting time and decreases the number on adhered platelets as compared to immobilization of heparin alone. 

The procedure used for determination of clotting time is a modification of a Lee-White Clotting Test. Before each test was undertaken, the surface of each sample was thoroughly washed with distilled water and oven dried. Blood used in these tests was obtained from a normal human volunteer and was used as drawn without citration. The twenty cc. of blood used for each test were drawn from an antecubital vein. In order to ensure that the blood which was used in each test was of a low tissue thromboplastin concentration, a two syringe technique was used and only the last 6 cc. of blood taken were used in the test the first 14 cc. were discarded. Time measurement was started as soon as the blood entered the tube and stopped upon the onset of clot formation. Occasionally, when the sample was observed not to have clotted within thirty minutes, a portion of the blood was removed from the tube and placed on a piece of gauze and carefully examined for slight evidence of clot formation. The samples which were used for the above test were as follows ... 

The use of pharmacodynamic end points for high-dose selection is considered to be highly compound specific and is considered for individual study designs on the basis of scientific merit. The high dose should produce a pharmacodynamic response in the test species that precludes further dose escalation but does not produce disturbances of physiology or homeostasis that would compromise the validity of the carcinogenicity study. Examples of such pharmacodynamic endpoints include hypotension and inhibition of blood clotting. 

The standard test procedures described below have been established to assess pharmacological and safety features of chemical compounds, such as drugs and newly introduced excipients. With some qualifications these tests are also used for biological pharmaceuticals, which act pharmacologically (as opposed to an immunological mode of action) and are applied frequently or in regular, short intervals, e.g. cytokines or blood clotting factors. 

---