Prothrombin-antibody coexistent with lupus anticoagulant (LA): clinical study and immunochemical characterization

The patient is a 23 y.o. man with acute nephritis and bleeding at presentation. Laboratory data consistent with the diagnosis of systemic lupus erythematosus. A lupus anticoagulant was found: tissue thromboplastin inhibition test (TTIT) ratio 3.4; diluted Russell viper venom (DRVV) ratio 2.6. Hypoprothrombinemia (FII:C less than 1%; FIIR:Ag 5%) was present; prothrombin survival time (FII concentrate infusion 60 U/kg): t1/2 approximately to 9 hours. A prothrombin antibody was identified: it is not neutralizing but forms an immunecomplex with prothrombin. The antibody was characterized as IgG2, IgA, k, lambda. The prothrombin survival time indicates that the hypoprothrombinemia is due to the clearance of the prothrombin-antiprothrombin complex in vivo.