What are causes of an isolated elevation of activated partial thromboplastin time (aPTT) (normal prothrombin time [PT])

By William Aird

Deficiency or inhibitor of one or more components of the intrinsic pathway including contact pathway factor (especially FXII, but also HMWK and prekallikrein), FXI, FIX, and FVIII, or antibodies against phospholipids (lupus anticoagulant).

Isolated elevation in aPTT involves deficiency or inhibitors against factors of the intrinsic pathway (shown in red) or against phospholipids (lupus anticoagulant).