Post-natal development of factor IX.
Post-natal development of clotting activity and of antigen level of Factor IX was evaluated in 111 healthy, breastfed, newborn infants, aged 1-30 days. Of these, 80 had received at birth 2 mg of vitamin K1 orally. Factor IX clotting activity was determined by one-stage assay and antigen level by electroimmunoassay. On the 1st day both antigen level and clotting activity were low  and the ratio was 1.01. There was a significant postnatal increase of the two activities of Factor IX during the first three days of life; thereafter both remained constant. No statistical difference inFactor IX activity was found with oral administration of vitamin K1 after the birth. During the first month of life both clotting activity and antigen level of Factor IX were low as compared to adult values. There was no correlation with age. The Factor IX protein of newborns did not show molecular heterogeneity by crossed-immunoelectrophoresis.
D000941:Antigens / Q000032:analysis; D005164:Factor IX / Q000276:immunology / Q000502:physiology*; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D007231:Infant, Newborn; D014812:Vitamin K / Q000494:pharmacology
D000941:Antigens; D014812:Vitamin K; D005164:Factor IX