Congenital factor deficiencies
- Contact factors (no clinical bleeding)
- Factor XII (no clinical bleeding)
- Factor XI
- Factor IX (hemophilia B)
- Factor VIII (hemophilia A)
- Factor VIII (von Willebrand's disease)
- Factor I (afibrinogenemia)
Anticoagulants
- Factor VIII inhibitor (postpartum, idiopathic, or after factor VIII infusions)
- Lupus anticoagulant (no clinical bleeding)
- Heparin
- Warfarin (PT increased more than PTT)
Other
- Disseminated intravascular coagulation (PT & PTT increased)
- Liver disease (PT increased more than PTT)
- Vitamin K deficiency (PT increased more than PTT)