✅ Isolated elevation of aPTT indicates deficiency of, or inhibitor against one or more factors in the intrinsic pathway (FXII, FXI, FIX, FVIII).
✅ Isolated elevation of aPTT in a patient with thrombosis is a red flag for lupus anticoagulant.
✅ Isolated elevation of aPTT in a patient with recent onset of spontaneous bleeding is a red flag for acquired hemophilia A (autoimmune inhibition of FVIII activity).
✅ Failure of the elevated aPTT to correct with normal plasma (mixing study) indicates an inhibitor against one of the clotting factors in the intrinsic pathway, almost always FVIII.
✅ The diagnosis of acquired hemophilia A is confirmed by demonstrating reduce FVIII activity in a clotting factor assay.
✅ Acquired factor VIII can lead to life-threatening bleeding. Most cases require urgent measures to minimize bleeding, including either rFVII or aPCC/FEIBA (so-called bypassing agents).
✅ In addition, eradication of the inhibitor is a top priority and treatment with immunosuppressive agents (with steroids and cyclophosphamide or rituximab) should be initiated immediately.
✅ Treatment of the underlying causative condition, if present, should be undertaken.
✅ Invasive procedures should be avoided if at all possible.