Assay of factor IX antigen using an enzyme immuno assay.

An Enzyme Linked immuno Sorbent Assay (ELISA) was developed for the measurement of factor IX:Ag. The results obtained in 90 control subjects, 56 hemophilia B patients and 40 patients under oral anticoagulant treatment were compared with factor IX:C and factor IX:Ag levels according to Electro Immuno-Assay (EIA). In healthy volunteers the mean factor IX:C level was 106.7 U/dl, the mean factor IX:Ag level was 96.8 U/dl according to EIA procedure and 101.5 U/dl according to ELISA method. Using ELISA, 10 hemophiliacs had no detectable antigen, and 13 had minute amounts of IX:Ag. All these patients are classified as B-. Among the others 21 had reduced antigen and are considered as BR and 12 had normal level of IX:Ag and are B+. Patients taking oral anticoagulants had not only a decreased factor IX:C level but also a reduced factor IX:Ag level which is always lower when using EIA procedure in the presence of EDTA than according to ELISA method.