Coagulation cascade refers to the molecular process by which the body forms clots to avoid hemorrhage. There are two major pathways by which coagulation occurs: the intrinsic and extrinsic pathways.
Here is a chart showing the two major pathways.
Major coagulation factors will be examined in the tests. The coagulation factors include bleeding time, thrombin time, the prothrombin time and activated partial thromboplastin time or partial thromboplastin time.
Bleeding time (BT): A normal bleeding time indicates adequate platelet hemostatic function.
Normal range: 3-9 minutes.
Thrombin time (TT): The test is used to assess if the common clotting cascade is intact downstream of both the extrinsic and intrinsic pathways (after their intersection at Factor Xa).
Normal range: less than 22 seconds (~14-16 seconds).
The prothrombin time (PT): The test is used to evaluate the extrinsic pathway of coagulation.
Normal range: INR of 0.8-1.2 (2.0-3.0 desired for patients on Warfarin).
Activated partial thromboplastin time (APTT) or partial thromboplastin time (PTT): The tests are used to assess if the intrinsic pathway is intact.
Normal range: 30-50 seconds.
Keywords: coagulation cascade