Determining the significance of anti-Kl 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 fathers. Forty-seven were K - 1 and 17 were K1,2; 21 were unavailable. Antibody titers were done on the mothers in the latter two groups. Women with titers 32 had amniocentesis performed for optical density values (AOD450) 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 (DAB). We conclude that titration studies are reliable tools to evaluate anti-K1 sensitization when the titer is <32. Cordocentesis can detect antigen-negative fetuses, which then reduces the need for titrations and amniocentesis.