Hema Lec2

• Hemostasis involves the interaction of blood vessels, platelets, the coagulation mechanism, fibrinolysis and tissue repair.
• Hemostasis is a complex process that produces a clot to stop the bleeding, keeps the clot confined, and dissolves the clot as the wound heals.
• Extravascular Tissue Factor/ TF is a tissue surrounding the vessel.
• Vascular Intima is a blood vessel through which the blood flows.
• Intrvascular Component is plasma proteins and platelets, including coagulation factors, inhibitors of coagulation, inhibitors of fibrinolysis, factors of fibrinolysis, Ca++, vWF, platelets.
• The concept of normal coagulation involves the balance between platelets, coagulation, and fibrinolysis.
• Hypercoagulation is characterized by uncontrolled production of thrombi.
• Hypocoagulation is characterized by poor clot formation and excessive fibrinolysis.
• Thrombosis is the formation and dissolution of thrombi maintained in a delicate balance.
• Bleeding is the absence of thrombi.
• Platelets are multinucleated and stimulated by thrombopoietin (TPO).
• Platelets are not cells but fragments of megakaryocyte cytoplasm.
• The normal platelet count is 150 - 400 x 10^3 / uL.
• Platelets circulate in the blood for 10 days.
• Laboratory Evaluation: Activation of Common Pathway and Conversion of Prothrombin to Thrombin can be tested in Phase II and III of Coagulation.
• Activated Recalcification Time is a more sensitive method than the coagulation time of whole blood.
• Activated Coagulation Time of Whole Blood is the time necessary for fresh blood to form a clot when incubated at 37 C° in the presence of "surface contact" activation.
• Activated Recalcification Time makes use of 0.25 M • CaCl2 as activator.
• Lee-White Method or Whole Blood Clotting Time is the time required for freshly collected blood to form a firm clot in standardized glass tubes at 37 C°.
• Common Pathway starts with the activation of Factor X to Factor Xa by either intrinsic or extrinsic pathway.
• Normal Value for Activated Recalcification Time is less than 50 seconds.
• The Coagulation Test tests the composite action of all plasma factors acting simultaneously.
• Clotting time is a measure of the ability of the blood to clot and is not influenced by the platelet functions other than PF3.
• The "Contact Factor" is activated along with Factor XII, HMWK, and prekallikrein in the Intrinsic Pathway.
• Clotting time measures only the time required for the formation of the traces of thrombin sufficient to produce a visible clot.
• Macro Methods are superior for there is less contamination of the plasma with tissue fluids when blood is drawn from a vein.
• Substitution tests can be adopted if primary tests like PT or APTT are abnormally prolonged and indicate a factor deficiency.
• Fit is a rapid slide test based on the agglutination of fibrinogen-coated red blood cells by the latex anti-human fibrinogen reagent.
• If the original prolonged APTT or PT indicates that the deficient factor has been added to the patient’s plasma by substitution solutions, a correction is made as follows:
• Fibrindex Test is a commercially available test wherein upon addition of plasma containing fibrinogen, thrombin produces clotting.
• Aged plasma lacks labile factors V & VII but retains normal activity of all coagulation factors.
• In substitution tests, the patient’s deficient plasma is diluted 1:1 with a plasma or serum substitute and the APTT or PT is repeated.
• Fresh adsorbed plasma lacks vitamin K dependent factors (II, VII, IX, X) but retains activity of all other coagulation factors.
• Aged serum lacks factors I, II, V, VII but retains normal activity of all coagulation factors.
• Thrombin Time is a test for the deficiency or inhibition of fibrinogen.
• Prothrombin time ratio is defined as the prothrombin time ratio had the test been performed using international standard thromboplastin reagent.
• Fibrinogen Titer Method involves serial dilutions of plasma diluted with thrombin, and the titer is the highest dilution in which a fibrin clot can be seen, related to the fibrinogen concentration and indirectly to the presence of circulating anticoagulants.
• Factors that affect bleeding time include the elasticity of the cut tissue, the ability of the blood vessels to constrict and retract, and the mechanical and chemical action of platelets in the formation of a hemostatic plug.
• Platelet count can be determined using an indirect method where platelets are counted in their relationship to red cells on a fixed-stained smear.
• This method of platelet count is not reliable because the results depend upon the distribution of platelets and the red cell count.