Thrombin time

Discussion in 'Step I' started by aspiringmd1015, Aug 17, 2015.

  1. aspiringmd1015

    2+ Year Member

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    can someone explain thrombin time?
     
  2. Keto

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    [​IMG]
    • Intrinsic pathway - aPTT
      contact factors, XI, XII, VIII, IX

    • Extrinsic pathway - PT
      TF, VII

    • Common pathway
      X, V, Prothrombin (II) → Thrombin;
      Fibrinogen (I) activated by Thrombin→ Initial Fibrin clot; Factor XIII → Cross-linked fibrin clot.


    The thrombin-time (TT) measures the final step in the common pathway (Fibrinogen → Fibrin). This is tested and measured by adding exogenous thrombin (this can be bovine or human thrombin) to the plasma in the laboratory setting. The time to form a clot is then recorded. Normal values are around 20-38 sec.


    What causes a prolonged TT?
    • Heparin (through ATIII → inactivation of thrombin; this will also inhibit the added exogenous thrombin)
    • Direct thrombin inhibitors: Hirudin, Argatroban (this will also inhibit the added exogenous thrombin)
    • Fibrinogen deficiency: Hypofibrinogenemia, if fibrinogen was used up, newborns (can have a not fully functioning fibrinogen)
    • Fibrin or fibrinogen degradation products (they will inhibit thrombin)
    • High concentration of serum proteins (MM) (inhibit the polymerization of fibrin)
    • If there are antibodies against bovine thrombin (if patient was previously exposed f.e. during surgery and you test with bovine thrombin)
    • ....

    Hope this helps.
     
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  3. Phloston

    Physician Lifetime Donor Verified Account 5+ Year Member

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    Thanks for the post :)
     
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