Hemolytic disease of the newborn (anti-Kell)

Hemolytic disease of the newborn (anti-Kell₁) is the second most common cause of severe hemolytic disease of the newborn (HDN) after Rh disease. Anti-Kell₁ is becoming relatively more important as prevention of Rh disease is also becoming more effective.

Hemolytic disease of the newborn (anti-Kell₁) is caused by a mismatch between the Kell antigens of the mother and fetus. About 91% of the population are Kell₁ negative and about 9% are Kell₁ positive. A fraction of a percentage are homozygous for Kell₁. Therefore, about 4.5% of babies born to a Kell₁ negative mother are Kell₁ positive.

The disease results when maternal antibodies to Kell₁ are transferred to the fetus across the placental barrier, breaching immune privilege. These antibodies can cause severe anemia by interfering with the early proliferation of red blood cells as well as causing alloimmune hemolysis. Very severe disease can occur as early as 20 weeks gestation. Hydrops fetalis can also occur early. The finding of anti-Kell antibodies in an antenatal screening blood test (indirect Coombs test) is an indication for early referral to a specialist service for assessment, management and treatment.