Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (819 page)

   
High molecular weight kininogen and prekallikrein
(Fletcher factor): Clotting factors that activate the early phase of the intrinsic pathway and the complement system. May prolong PTT (not PT) when decreased. No bleeding diathesis associated with their congenital deficiencies.

   
Factor XIII
(fibrin-stabilizing factor): Synthesized in the liver; also present in platelets. Stabilizes polymerized fibrin in the presence of calcium. Its deficiency does not affect PT (INR) or PTT. In its absence, clots are soluble in 5-molar urea.

   
Normal ranges:

   
Factors based on PT reagent
:

   Factor II: 70–120%

   Factor V: 70–150%

   Factor VII: 70–150%

   Factor X: 70–150%

   
Factors based on PTT reagent:

   Factor VIII: 70–150%

   Factor IX: 70–120%

   Factor XI: 60–120%

   Factor XII: 60–150%