Mixing Test in a Case of Combined Acquired Hemophilia A and Coagulation Factor Deficiency: A Case Report

Acquired hemophilia A and B are rare autoimmune disorders where antibodies inhibit coagulation factors VIII and IX, leading to excessive bleeding. Acquired hemophilia displays an <i>inhibitor pattern</i> in mixing tests. Meanwhile, coagulation factor deficiency, often due to liver disease, results from reduced synthesis of coagulation factors and shows a <i>deficiency pattern</i> in mixing tests. However, overlapping features can complicate differentiation. A <i>percent correction </i>method in the mixing test improved accuracy in distinguishing between the <i>inhibitor pattern</i> and the <i>deficiency pattern</i>. Using this method, a complex case involving both acquired hemophilia A and liver-related coagulation factor deficiency was successfully diagnosed. A 70-year-old man presented with subcutaneous, intracranial bleeding, and gastrointestinal hemorrhage. The laboratory data revealed severe anemia (hemoglobin 5.7 g/dL) without thrombocytopenia. Coagulation studies showed significantly prolonged activated partial thromboplastin time (APTT >100 seconds), mildly prolonged prothrombin time (PT 13.0 seconds), and a low fibrinogen (144 mg/dL). Given the disproportionately prolonged APTT, we performed a 1:1 <i>percent correction</i> of the mixing test, which revealed a <i>deficiency pattern</i> before treatment. We administered fresh frozen plasma (FFP); however, the coagulopathy was not improved. After the FFP treatment, the mixing test revealed a <i>deficiency pattern</i> in the early phase and an <i>inhibitor pattern</i> in the late phase. The coagulation factors were nonspecifically decreased. The inhibitor for coagulation factor VIII was identified. We diagnosed the patient with acquired hemophilia. Diagnosing coagulopathy is especially challenging when a patient has both acquired hemophilia and coagulation factor deficiency, as mixing test patterns may overlap and lose distinct characteristics. The 1:1 <i>percent correction</i> method proved to be the most reliable approach for distinguishing between deficiency and inhibitor-related patterns. In this case, acquired hemophilia A was the primary cause of severe bleeding with underlying coagulation factor deficiency. Combining mixing tests with plasma supplementation helped clarify the dual pathogenesis.