Prothrombin Time (PT) (Last Updated - 3/5/2005)

-measured by drawing blood with EDTA (prevents clotting via calcium binding)
-then re-calcifying the blood in the lab and adding thromboplastin --> contains phospholipids & tissue factor (TF or Factor III)
-normal blood should clot following the above process in 12-14 s.
-PT will be prolonged with extrinsic pathway dysfunction b/c thromboplastin is extrinsic to plasma

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References:

Goodman & Gilman's: The Pharmacologic Basis Of Therapeutics - 10th Edition - 2001. Chapter 55.