A 26 years old female suffers from PPH on her second postnatal day. Her APTT is prolonged while bleeding time and prothrombin time and platelet count are normal. Likely diagnosis is:

This is a case of acquired hemophilia A. Approximately 50 percent of acquired hemophilia A patients have an underlying condition, such as an autoimmune disorder (e.g., rheumatoid ahritis or systemic lupus erythematosus), malignancy, pregnancy, or a history consistent with a drug reaction. Patients with acquired hemophilia A have a prolonged aPTT caused by decreased or absent factor VIII activity in the intrinsic pathway of blood coagulation. The diagnosis of acquired hemophilia A is made by the demonstration of a solitary prolonged activated paial thromboplastin time (aPTT) that fails to correct on mixing with equal volumes of normal plasma (50:50 mix). The prothrombin time (PT), thrombin time (TT), and fibrinogen activity are all normal. Specific factor assays then are performed to determine whether a specific coagulation factor inhibitor or a lupus anticoagulant is present. Ref: Lollar P. (2010). Chapter 128. Antibody-Mediated Coagulation Factor Deficiencies. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.