Bleeding time

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  1. Each phase of hemostasis can be evaluated: 1) formation of hemostatic plugs (bleeding time); 2) generation of thrombin (PT and PTT); 3) the thrombin-fibrinogen reaction and stability of the fibrin clot (thrombin time)
    1. formation of hemostatic plug – bleeding time
      1. screens for overall adequacy of formation of hemostatic plugs independent of blood coagulation factors (upper limit of normal = 7.5 minutes)
        1. most common cause of elevation is aspirin or non-steroidal use, uremia, vW disease, disorders of platelet function
          1. treatment for vonWillibrand’s disease is cryoprecipitate or DDAVP for a small surgery (cryoprecipitate contains vW factor, factor VIII, and fibrinogen)
    2. formation of fibrin
      1. PTT (intrinsic) – screens for abnormalities of the blood coagulation reactions triggered by exposure of plasma to a negatively charged surface – measures fibrinogen (factor I), prothrombin (factor II), factors V, VIII, IX, X, XI, XII, prekalikrein, high molecular weight kininogen – normal PTT is 28-34 seconds
      2. PT (extrinsic) – screens for abnormalities of the blood coagulation reactions triggered when blood is exposed to tissue factor reagents (thromboplastin –factor III) – measures extrinsic pathway factors V, VII, X, prothrombin, and fibrinogen – normal 10-12 seconds
        1. Sensitive test for liver disease, vitamin K deficiency and DIC
        2. Factors II, VII, IX and X are vitamin K dependent
    3. thrombin-fibrinogen reaction and stability of fibrin clot
  2. regulation of blood coagulation can also be measured by checking levels of antithrombin III and protein C and S
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