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 inhibitor pattern in mixing tests. Meanwhile, coagulation factor deficiency, often due to liver disease, results from reduced synthesis of coagulation factors and shows a deficiency pattern in mixing tests. However, overlapping features can complicate differentiation. A percent correction method in the mixing test improved accuracy in distinguishing between the inhibitor pattern and the deficiency pattern. 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 percent correction of the mixing test, which revealed a deficiency pattern before treatment. We administered fresh frozen plasma (FFP); however, the coagulopathy was not improved. After the FFP treatment, the mixing test revealed a deficiency pattern in the early phase and an inhibitor pattern 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 percent correction 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.