TAKE HOME POINTS 

How do approach elevated PT/INR, or PTT of unknown etiology

-Do Mixing study to see if it corrects (deficiency) or doesn’t correct (inhibitor)
-PT=Play Tennis OUTSIDE=Extrinsic pathway
-PTT=Play Table Tennis INSIDE=Intrinsic pathway
-Most common inhibitor is Factor 8 inhibitor causing elevated PTT

Causes of elevated PTT

-Involves Factor 8, 9, or 11
-Iatrogenic causes include heparin, LWMH
-Lupus anticoagulant (usually presents with thrombosis)

Risk factors for developing a Factor inhibitor

-Pregnancy, post-partum, RA,  malignancy, SLE, some drug reactions (Phenytoin/Penicillin)

Treatment

-Control bleeding (done via activated prothrombin complex concentrate like FEIBA or recombinant human factor VIIA)
-Eliminate inhibitor via immunosuppression (steroids +-rituximab +-Cytoxan)