Clotting time

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. 

Hematology. The functional status of blood and of the blood-forming tissues can be assessed by tests which include red and white blood cell counts, platelet counts, clotting time, coagulation tests, and examination of bone marrow. Such tests, in addition to detecting abnormahties, may also allow differentiation between primary and secondary effects on blood and blood-forming tissues (75). 

The classical method for the determination of vitamin K is based on the clotting time of a vitamin K-deficient chick. It is relatively easy to produce a hemorraghic state ia chicks (17). Vitamin K-deficient tats have also been used for this assay (18). Owiag to the development of modem chromatographic techniques, this method of analysis has been supplanted by other methodology. 

Haematological characteristics (haemoglobin level, red blood and white blood cell counts, platelet count, blood clotting time). 

Promoting an Optimai Response to Therapy Heparin preparations, unlike warfarin, must be given by the parenteral route, preferably SC or IV The onset of anticoagiilation is almost immediate after a single dose. Maximum effects occur witiiin 10 minutes of administration. Clotting time will return to normal witiiin 4 hours unless subsequent doses are given. 

Besides the changes in wettability, they found that the hemocompatibility was significantly affected by plasma treatment. Treatment of PDMS with both Ar and O2 induced a decrease in hemocompatibility, leading to shorter clotting times. The N2 and NH3 treatments had a significantly beneficial effect on the activation of the coagulation cascade. 

Vitamin K is an essential factor in the production of coagulation proteins within the liver. Elevated clotting times from decreased protein synthesis are indistinguishable from those produced by low vitamin K levels caused by malnutrition or poor intestinal absorption. Vitamin K (phytonadione) 10 mg subcutaneously daily for 3 days can help to establish whether the prolonged bleeding time results from loss of synthetic function in the liver or vitamin K deficiency. 

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. 

International Normalized Ratio (INR) The ratio of the patient s clotting time to the clinical laboratory s mean reference value normalized by raising it to the International Sensitivity Index (ISI) power to account for differences in thromboplastin reagents. Therefore, INR = (patient s prothrombin time/laboratory s mean normal prothrombin time)ISI. 

No. PET Sample Incorporated pHEMA (%) Clotting Time of Blood (min)... 

Blood that has been stored for 60 min in the presence of heparinized PET films (Sample ho. 4), when put into another glass vessel was clotted within 5 min, which is the clotting time of blood not exposed to heparinized materials (4). Therefore, any reduction in thrombus formation on the heparinized film surface can only be attributed to the activity of bound heparin, i.e. the free heparin was not eluted into the blood. 

More recently chitosan polymers which are derivatives of chitin materials have evoked interest due to their bioactivity and biodegradability. For example, N-carboxybutyl chitosan has been show to effectively promote wound healing (9). Acetate, and butyrate derivatives of chitosan have decreased blood clotting time significantly (10). 

E.J. Cohen, L.J. Camerlengo, and J.P. Dearing, Activated clotting times and cardiopulmonary bypass I. The effect of hemodilution and hypothermia upon activated clotting time. J. Extra Corpor. Technol. 12, 139-141 (1980). 

The last of the fat-soluble vitamins to be identified was vitamin K, found by Dam to be an anti-hemorrhagic factor for young chicks, distinct from vitamin C. Its structure was determined by Dam in collaboration with Karrer. Interest in the vitamin was intensified when it was discovered (Link, 1941) that dicoumarol, present in spoiled sweet clover, was the agent producing hypothrombinemia (giving prolonged blood-clotting time) in cattle. Since vitamin K is structurally similar to dicoumarol, the vitamin was presumptively implicated in thrombin formation. This has been fully substantiated by recent work on the role of vitamin K in the synthesis of prothrombin in the liver. 

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