Activated Partial Thromboplastin Time (aPTT or PTT) (Last Updated - 2/25/2005)

-measured by drawing blood with EDTA (prevents clotting via calcium binding)
-then re-calcifying the blood in the lab and adding negatively-charged phospholipids and kaolin (aluminum silicate)
-normal blood should clot following the above process in 26-33 s.
-aPTT or PTT will be prolonged with intrinsic pathway dysfunction b/c all components of the PTT are intrinsic to plasma (except kaolin)

========================================================
References:

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