Abstract: Objective To explore the detection method of low-frequency antigen antibody anti-McCb in a case of hemolytic disease of the fetus and newborn. Methods In this case, the infant developed jaundice 24 hours after birth, which raised suspicion of neonatal hemolytic disease caused by unexpected antibodies other than those of the ABO blood group. The mother's serum showed no reaction with panel cells, so it was necessary to confirm whether the father's red blood cells expressed a certain low-frequency antigen. Therefore, the mother's serum was reacted separately with the father's and the infant's red blood cells. The positive results indicated the presence of antibodies in the mother's serum targeting a certain low-frequency antigen on the father's and the infant's red blood cells. Different enzymes or chemical reagents were used to treat the father's red blood cells, creating different reaction patterns for high-frequency and low-frequency antigens under various enzymes, thereby further identifying the specific antigens and antibodies. Results It is highly suspected that the neonatal hemolytic disease is caused by anti-McCb antibodies. Conclusion PEG enhancement test and enzyme treatment technology are helpful to the detection of anti-low frequency antigen antibodies, and molecular biological methods are still needed for confirmation.

Key words: Low frequency antigenic antibody, Knops blood group system, Enzyme treated cell, Anti-McCb