Haem Measurement – Coagulation

What is tested

Extrinsic pathway
Final pathway

Intrinsic pathway
Final pathway

Principles

• Citrate added to chelate calcium
• Sample centrifuged to give plasma
• Calcium returned at time of testing
• Tissue factor added
  • Binds to VIIa, activating X
• Time until coagulation measured

• Citrate added to chelate calcium, calcium returned at time of testing
• Sample centrifuged to give plasma
• Calcium returned at time of testing
• Kaolin added
  • Activates factor XII
• Cephalin added
  • Provides phospholipid surface for binding of tenase and prothrombinase complexes
• Time until coagulation measured

Normal Values

11-13 seconds

30-40 seconds

Causes of Prolonged Time

• Reduction in functional VII
  • Warfarin
  • Liver disease
• Factor X deficiency
  • DIC

Heparin
Haemophilia
DIC
Liver disease

Uses

Warfarin monitoring
Screening test for coagulopathy

Heparin monitoring
Screening test for coagulopathy

What is tested

Entire clotting cascade and platelet function

Entire clotting cascade and platelet function

Principles

• Whole, fresh blood is added to a clotting activator (e.g. kaolin)
• Time until coagulation measured

• Citrate added to chelate calcium, calcium returned at time of testing
• Sample injected into the sampling cup (containing a clotting activator)
• The cup is rotated around a pin, or the pin rotated independently
• As a clot forms, the pin’s movement is restricted by adherence to it
• This restriction is outputted graphically

Normal values

100-110 seconds

Based on test – TEG/ROTEM

Causes of prolonged time

Any coagulopathy, e.g.
• Clotting factor inhibitors e.g. warfarin, heparin
• Thrombocytopaenia or platelet inhibitors
• DIC

R time – clotting factors
α angle – fibrinogen function and preactivation
MA – platelet number and function
CLT – effectiveness of fibrinolysis

Uses

Monitoring adequacy of coagulation in cardiopulmonary bypass, ECMO, dialysis

Trauma – assess need for blood product replacement
Theatre monitoring
• Cardiac surgery
• Liver transplant