Red Cell D Antigen Sites and Titration Scores in a Family with Weak and Normal Du Phenotypes Inherited from a Homozygous Du Mother

The family of an obstetrical patient with an unusually weak Du phenotype has been studied. Strong positive reactions in the Du test were observed with the cells of four siblings who are of the DucE phenotype whereas very weak reactions were obtained with the proposita and one sib who are DuCe. The father is Rh negative thus proving the mother to be homozygous Du (DuCe/DucE). The two Du phenotypes and the homozygous Du mother were compared by titration scores and by the uptake of labeled anti‐D. The correlation was good between the titration score and the number of D antigen sites. However, red blood cells with normal D antigen content and one of the two weakly reactive DuCe/dce cells had titration scores that were too low in comparison to the number of D sites.