Initiation substances activate s by proteolysis a cascade of circulating precursor proteins which leads to the generation of thrombin which in turn converts

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  • Initiation substances activate s by proteolysis a cascade of circulating precursor proteins which leads to the generation of thrombin which in turn converts soluble fibrinogen into fibrin.
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  • Tests of Coagulation 1. Prothrombin Time (PT): Tests the extrinsic & common pathways = Factors (VII) & (X, V, Prothrombin & fibrinogen). = Factors (VII) & (X, V, Prothrombin & fibrinogen). Normal = 10 14 sec. Test: Plasma + calcium + brain extract (thromboplastin)
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  • Tests of Coagulation (Cont ) 2. Activated Partial Thromboplastin Time (APTT) or (PTT): Tests intrinsic pathways (VIII, IX, XI, XII) & common pathway (X, V, prothrombin, fibrinogen). Normal = 30 40 sec. Test: Plasma + calcium + phospholipid + Kaolin (activates contact factors) 3. Thrombin Time: Tests for fibrinogen Normal = 10 12 sec.
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  • Tests of Coagulation (Cont ) 4. Specific Factor Assay: Functional Assay: Based on PTT or PT Tests principle: Plasma deficient in suspected factor + patients plasma (A) patients plasma (A) Plasma deficient in suspected factor + normal plasma (B). plasma (B). The corrective effect of (A) is compared to (B) and the result is expressed as percentage of normal activity. 5. Immunological Assay Available for some coagulation factors
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  • Hereditary Coagulation Disorders Hereditary deficiencies of coagulation factors are rare. However, the following disorders are more common: Hemophilia A (Factor VIII deficiency) Hemophilia B (Christma s disease) (Factor IX deficiency) Von Willebrand s disease
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  • Hemophilia A This is the most common hereditary disorder of blood coagulation. Inheritance: X-linked Defect: The absence or low level of factor VIII (clotting activity [VIII : C])
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  • Correlation of Coagulation Factor Activity & Disease Severity in Hemophilia & Factor IX Deficiency Coagulation Factor Activity (% of normal)