Jun 30, 2015
70
92
Zurich, Switzerland

  • 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.
 

Phloston

Lifetime Donor
7+ Year Member
Jan 17, 2012
3,709
1,487
Osaka, Japan
mehlmanmedical.com

  • 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.
Thanks for the post :)
 
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