Hemolytic Disease Fetal Newborns
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Publicado: 24 de noviembre de 2012
Hemostasis Online Lab- Prothrombin Time Test
Tissue factor from many organs markedly enhances the activity of factor VII. Saline extracts of tissue contain a lipid moity essential in thecoagulation cascade.
Prothrombin time is affected by: Prothrombin concentration (factor II), fibrinogen conc,, factors V, X, VII. It can also be prolonged by the presence of high concentrations of heparin.The Extrinsic Pathway is what is measured by the prothrombin time test. They call it intrinsic because it needs tissue factor no found in the blood stream to initiate the series of reactions.Thromboplastin reagent: Usually rabbit brain or a combo of brain and rabbit lung. Brain tissue is preferred because it is more easily free of contaminants.
The reagent is made by blending the braintissue with saline. Depending on the type of tissue used and the dilution of the saline the test results will be different. Because of this and the fact that each hospital uses it’s own reagent itis not possible to compare results from one hospital lab to another.
Clinical importance of prothrombin time: The time is used to monitor treatment with warfarin (an oral anticoagulant). Warafincompetes with Vitamin K in the liver. It prevents the normal carboxylation of glutamic acid residues at the amino terminal end of the Vitamin K dependent factor molecules. This results in functionaldeficiency of factors II, VII, IX, X, protein C and S. This is a problem because prothrombin time is sensitive to deficiencies of factor II, VII and X.
The prothrombin time will be prolonged withsingle factor deficiencies when the levels of factor II, V, VII, and X drop below 20-30% of the normal mean, and when the fibrinogen concentration is somewhat less than 0.10 g/dL. Normal values for theprothrombin time at Fairview are 8.9-10.7 seconds. (INR 0.89-1.09)
It is important to remembe that different lot #’s of thromboplastin yeild slightly different answers. So every time a lot number...
Tissue factor from many organs markedly enhances the activity of factor VII. Saline extracts of tissue contain a lipid moity essential in thecoagulation cascade.
Prothrombin time is affected by: Prothrombin concentration (factor II), fibrinogen conc,, factors V, X, VII. It can also be prolonged by the presence of high concentrations of heparin.The Extrinsic Pathway is what is measured by the prothrombin time test. They call it intrinsic because it needs tissue factor no found in the blood stream to initiate the series of reactions.Thromboplastin reagent: Usually rabbit brain or a combo of brain and rabbit lung. Brain tissue is preferred because it is more easily free of contaminants.
The reagent is made by blending the braintissue with saline. Depending on the type of tissue used and the dilution of the saline the test results will be different. Because of this and the fact that each hospital uses it’s own reagent itis not possible to compare results from one hospital lab to another.
Clinical importance of prothrombin time: The time is used to monitor treatment with warfarin (an oral anticoagulant). Warafincompetes with Vitamin K in the liver. It prevents the normal carboxylation of glutamic acid residues at the amino terminal end of the Vitamin K dependent factor molecules. This results in functionaldeficiency of factors II, VII, IX, X, protein C and S. This is a problem because prothrombin time is sensitive to deficiencies of factor II, VII and X.
The prothrombin time will be prolonged withsingle factor deficiencies when the levels of factor II, V, VII, and X drop below 20-30% of the normal mean, and when the fibrinogen concentration is somewhat less than 0.10 g/dL. Normal values for theprothrombin time at Fairview are 8.9-10.7 seconds. (INR 0.89-1.09)
It is important to remembe that different lot #’s of thromboplastin yeild slightly different answers. So every time a lot number...
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