Thrombosis and Hemostasis

Acquired factor XIII (FXIII) deficiency due to autoantibody against FXIII is a very rare severe hemorrhagic diathesis. Antibodies directed against theAsubunit of FXIII, which interfere with different functions of FXIII, have been described. Here, for the first time, we report an autoantibody against the B subunit of FXIII (FXIII-B) that caused lifethreatening bleeding in a patient with systemic lupus erythematosus. FXIII activity, FXIII-A2B2 complex, and individual FXIII subunits were undetectable in the plasma, whereas platelet FXIII activity and antigen were normal. Neither FXIII activation nor its activity was inhibited by the antibody, which bound to structural epitope(s) on both free and complexed FXIII-B. The autoantibody highly accelerated the elimination of FXIII from the circulation. FXIII supplementation combined with immunosuppressive therapy, plasmapheresis, immunoglobulin, and antiCD20 treatment resulted in the patient’s recovery. FXIII levels returned to around 20% at discharge and after gradual increase the levels stabilized above 50%. (Blood. 2009; 113:723-725)