Autoimmune factor XIII deficiency with unusual laboratory and clinical phenotype.

Hemorrhagic diathesis due to anti-factor XIII (FXIII) autoantibody is a rare but severe disorder. Challenges of the diagnosis and treatment is demonstrated by the case of a 67-year-old female without previous bleeding history, who suffered a huge muscular hematoma. Without bank subtraction 18% plasma FXIII activity was measured, however after correction for blank the activity was below the limit of detection and the lack of fibrin cross-linking in the patient's plasma confirmed the latter result. FXIII-A2 antigen was not detectable by ELISA, however it was well detected by western blotting. The autoantibody showed high affinity toward FXIII-A2 . Its considerable inhibitory activity was demonstrated by high titer in Bethesda units and the low IgG concentration required for inhibition. The main biochemical effect was the inhibition of Ca(2+) -induced activation. Eradication therapy was only partially successful. Four months after the last hemorrhagic event the patient suffered deep vein thrombosis complicated by pulmonary embolism.