Clotting screen
components
- Activated prothrombin time, APTT
- Prothrombin Time, PT
APTT
Kaolin added
Intrinsic pathway
Used to monitor heparin therapy
tests factors: I, II, V, VIII, IX, XI, XII
Prolonged in:
- Heparin therapy
- Haemophilia
- Disseminated intravascular coagulation
- Liver failure
- +/- von Willebrand disease
- presence of factor inhibitor
prothrombin time
Used to derive INR
Extrinsic pathway
tests factors: I, II, V, VII, X
PT prolonged:
- liver dysfunction (i.e. synthetic failure)