Step I Thrombin time

[aspiringmd1015]

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can someone explain thrombin time?

 

[Keto]

• 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]

• 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 🙂