Detection of Carriers of Haemophilia B

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Abstract
Plasma levels of factor IX activity and factor IX antigen were determined in 18 definite carriers of hemophilia B-, 10 definite carriers of hemophilia B+ and 40 control subjects. Factor IX antigen was determined by the electroimmunoassay technique of Laurell using a rabbit antiserum against factor IX. In hemophilia B-, statistical tolerance regions were constructed containing 90% of the factor IX activity and factor IX antigen values for the carriers and the control subjects. Of the 18 carriers, 10 were outside the tolerance region for control subjects; of the 40 control subjects, 17 were outside the tolerance region for the carriers. A better separation of the probabilities of being a carrier was obtained for the B- carriers and the control subjects when factor IX antigen was determined in addition to factor IX activity. In hemophilia B+, factor IX antigen was present in excess of factor IX activity in 9 of the 10 carriers. The values for factor IX activity and factor IX antigen for these 9 carriers fell outside the 90% tolerance region for the control subjects. The quantitative determination of factor IX antigen may be of value in the detection of carriers of hemophilia B+ and hemophilia B-.