A 47-year-old man having a chronic liver disease developed uncontrollable bleeding which was due to an inhibitor to factor XIII (F.XIII). The inhibitor was demonstrated by ready solubility in 2% monochloroacetic acid of the fibrin clot obtained from the mixture of normal and the patient plasma, and by absence of gamma-dimer and alpha-polymers in SDS-polyacrylamide gel electrophoresis of the clot. The inhibitor suppressed the transamidase activity of activated F.XIII and did not affect the activation of F.XIII by thrombin. A neutralization test showed that the inhibitor was an antibody of polyclonal IgG, and isolated IgG from the patient plasma exhibited the inhibitor activity. The patient plasma contained almost normal levels of F.XIII a and b subunit antigens, and Sephadex G-200 gel filtration of the plasma revealed that there was intact F.XIII separable from the inhibitor. These findings were interpreted that the inhibitor interacts not with the zymogen form but with the activated form of F.XIII.
These have been ten fully documented cases of inhibitor to F.XIII. Many of them had been treated with isoniazid, which is consequently thought to be related to the generation of the inhibitor. Our patient had not received such a drug and the cause is unknown.
