Abstract
This report presents the first prospectively followed case of hemolytic disease of the newborn due to anti-Jk3 alone. A Samoan woman with known anti-Jk3 was closely monitored during her third pregnancy. Because of elevated ∆OD values in the amniotic fluid and rising titer of serum antibody, labor was induced at 36 weeks gestation. The cord red blood cells were coated with IgG, and anti-Jk3 was eluted from the cord cells and the placenta. A family study was done quantitating the expression of Kidd antigens by titrations and scores. Although titrations and scores have been reported to identify cells carrying the silent allele Jk in the heterozygous state, in this family, dosage differences were noted with only 1 of 2 Jk-heterozygous daughters.