title: Acquired haemophilia A: errors in the diagnosis.
abstract: The distinction between a specific factor inactivator and a non-specific inhibitor is important when confronted by a patient with a history of bleeding and abnormal in-vitro coagulation tests. We report on two patients who presented with bleeding and a prolonged activated partial thromboplastin time. Initial factor assays suggested combined deficiency of factors VIII and IX as a result of the presence of inactivators. The use of dilution studies, chromogenic assays, a novel in-house enzyme-linked-immunosorbent-assay-based technique and phospholipid neutralization, demonstrated that Case 1 had a genuine factor VIII inactivator resulting in factor VIII levels of less than 1 IU/dl but no factor IX deficiency. Case 2 had normal levels of factor VIII on further testing and no specific inactivator to either factor VIII or IX but a potent antiphospholipid antibody which had interfered with the phospholipid-dependent in-vitro assays. Care must be taken in the interpretation of laboratory assays in the presence of antiphospholipid antibodies to ensure that the correct diagnosis is made and inappropriate treatment avoided.
authors.affiliation: Reference Centre for Haemostatic and Thrombotic Disorders, St. Thomas' Hospital, London, UK.
authors.forename: M A
authors.initials: MA
authors.lastname: Kazmi
authors.forename: W
authors.initials: W
authors.lastname: Pickering
authors.forename: M P
authors.initials: MP
authors.lastname: Smith
authors.forename: L J
authors.initials: LJ
authors.lastname: Holland
authors.forename: G F
authors.initials: GF
authors.lastname: Savidge
mesh_terms: D000328:Adult; D000368:Aged; D000906:Antibodies / Q000276:immunology; D017152:Antibodies, Antiphospholipid / Q000276:immunology*; D003937:Diagnosis, Differential; D005164:Factor IX / Q000276:immunology; D005169:Factor VIII / Q000276:immunology*; D005260:Female; D006467:Hemophilia A / Q000097:blood / Q000175:diagnosis* / Q000276:immunology*; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000175:diagnosis* / Q000276:immunology*; D008297:Male; D012680:Sensitivity and Specificity
chemical_list: D000906:Antibodies; D017152:Antibodies, Antiphospholipid; D005169:Factor VIII; D005164:Factor IX