Determining the significance of anti-K1 in hemolytic disease of the newborn (HDN)

Anti-K1 is capable of causing severe hemolytic disease of the newborn (HDN), but few cases are seen due to the low frequency of the antigen. A total of 1,215 pregnancies from 1962 to 1989 were reviewed. There were 404 non-anti-D clinically significant antibodies, of which 103 (25%) were anti-K1. Anti-K1 was detected in nine of the women at delivery, of whom two had antigen-positive infants who were clinically unaffected. Antigen typing was done on 64 of the 85 lathers. Forty-seven were K: -1 and 17 were K: 1,2; 21 were unavailable Antibody titers were done on the mothers in the latter two groups. Women with titers < 32 were followed by titration studies; all delivered clinically unaffected infants, four of whom were K:l. Women with titers >32 had amniocentesis performed for optical density values (ΔOD₄₅₀) or, after November 1987, were offered an alternative test, cordocentesis, to type the fetus and to do hemoglobins if the fetus was antigen-positive. Two women had severely affected infants requiring multiple intrauterine transfusions starting at 20-23 weeks. Six others delivered antigen-positive infants who did not require transfusions, although all had positive direct antiglobulin tests (DATs). We conclude that titration studies are reliable tools to evaluate anti-K1 sensitisation when the titer is < 32. Cordocentesis can detect antigennegative fetuses, which then reduces the need for titrations and amniocentesis. Immunohematology 1991;2:40–42.