Relationship of Factor IX Antigen and Coagulant in Hemophilia B Patients and Carriers

Summary

A neutralizing and precipitating monospecific antiserum to human factor IX was developed. Plasmas from 224 hemophilia B patients, 39 obligatory and 38 possible carriers were studied by coagulant assays and Laurell’s electroimmunoassays. Based on factor IX coagulant (IX-C) to IX antigen (IX-Ag) ratios, the patients were classified as being either concordant (ratios ≥0.71) or discordant (<0.71). The diagnostic classification into concordant and discordant patterns is difficult in patients with low levels of antigen where the two forms may merge due to the insensitivity of the assay below 12%. Of the total cases studied by us, 36% were discordant (excess antigen). This is in agreement with 33.66%, a composite figure representing 199 cases described in five recently published papers, and indicates that approximately one-third of the hemophilia B population is of the discordant type. The pattern, when established, was found consistent in each kinship studied.

Crossed antigen-antibody electrophoresis did not reveal any abnormalities in the hemophilia B plasmas with measurable IX-Ag.

We found a low incidence of the B_M variety. Determining this type of hemophilia B did not appear to increase the degree of predictability of the carrier state.

Studies of carriers demonstrated that immunologic techniques did not contribute to the predictability of the carrier state in pedigrees of the concordant variety. In the discordant group a factor IX-C/IX-Ag ratio of 0.7 or less indicated that a female was very likely to be a carrier. An improvement in the prediction of the carrier state in females of the discordant pattern was demonstrated.

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