Thanks for the post
- Intrinsic pathway - aPTT
contact factors, XI, XII, VIII, IX
- Extrinsic pathway - PT
- 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.