Prenatal diagnosis of hemophilia B by an immunoradiometric assay of factor IX
An immunoradiometric assay of factor IX was developed based on homologous antibodies that arose in a hemophilic patient. With this assay, 11 of 12 patients with severe hemophilia B had factor IX antigen levels below 1 U/dl and 6 patients with mild hemophilia B had various levels. Factor IX antigen in 8 fetuses (16th-20th gestational week) aborted for therapeutic reasons ranged from 1.8 to 10.0 U/d