Studies on vitamin K-dependent factor deficiency during early childhood with special reference to prothrombin activity and antigen level.

8 young infants aged 14 days to 5 months with vitamin K-dependent factor deficiency were studied with special reference to prothrombin activity and antigen level. Among them, 3 infants had congenital bile duct atresia and 5 were breast-fed babies with severe hemorrhagic tendency of unknown cause. In the patients with both congenital bile duct atresia and breast feeding the ratio of prothrombin activity to prothrombin antigen was lower than 0.1. Furthermore, the arc of prothrombin antigen in these patients demonstrated a faster anodal shift than did normal prothrombin antigen on crossed immunoelectrophoresis. This abnormal prothrombin antigen was not consumed after recalcification of patient plasma, and absorbed poorly on BaSO4. In addition, the abnormal prothrombin antigen disappeared from the patient plasma within a few days after parenteral administration of vitamin K. These results suggest that this abnormal prothrombin is PIVKA-II.