What is the significance of anti-k antibody?
Q: I found in my 3rd pregnancy that I have anti-k antibody. Therefore, my husband was tested for the antigen, which was positive. Has he always had this antigen and if so then why is the antibody showing in my blood now? What are the chances that the baby will also get the antigen?
A:The Kell antigen system (or the Kell-Cellano system) was named after the family of the antibody producer Mrs. Kellacher. It is a group of antigens on the red blood cells, which determine the Kell blood group type and also act as targets for some immune diseases, which result in red cell breakdown (haemolysis). Initially four antigens were described in this system: K or K1 (Kell) and k or K2 (cellano), and Kpa and Kpb. At present it comprises 22 blood group antigens with some showing a distinct racial prevalence (K antigen is more frequently found in Northern Europeans, the Jsa antigen is most frequently found in those of African descent and the Kpc antigen has been more frequently found in the Japanese). Kell allo-immunisation in women can be caused by pregnancy with a Kell-positive baby or, more commonly, following transfusion with Kell-positive blood i.e. individuals lacking a specific Kell antigen may develop antibodies against Kell antigens when transfused with blood containing that antigen or being exposed to red cells bearing that antigen. Subsequent blood transfusions may be marked by destruction of the new cells by these antibodies. People without Kell antigens (K0), must be transfused with blood from donors who are also K0 to prevent haemolysis. Autoimmune haemolytic anaemia (AIHA) occurs when the body produces an antibody against a blood group antigen on its own red blood cells. The antibodies lead to destruction of the red blood cells with resulting anaemia. Similarly, a pregnant woman may develop antibodies against fetal red blood cells resulting in haemolytic disease of the newborn (HDN). Both AIHA and HDN may be severe when caused by anti-Kell antibodies. You must have developed the antibodies during the previous pregnancy, as the baby must be Kell positive. During embryonic development the baby’s red cells enter the mother’s circulation via the placenta and trigger the production of antibodies. When these antibodies enter the baby’s circulation they bind to the Kell antigen present on the baby’s red cells leading to their breakdown. The ideal management of Kell haemolytic disease involves a multidisciplinary team effort by Obstetrics, Neonatology, Haematology and Transfusion services personnel. Efforts are directed at: 1) identifying which fetus is severely affected; 2) treating fetal anaemia; and 3) determining optimal time for delivery. Once anti-Kell antibodies are identified in a pregnant woman, the titers should be measured, history of previous pregnancies and blood transfusions ascertained, and the Kell status of the husband determined. If the husband is Kell negative, the fetus will be Kell negative, and no further investigations are required. But if the husband is Kell positive, the Kell status of the fetus needs to be determined. This can be done by DNA analysis of fetal cells obtained by chorionic villus sampling as early as 10-12 weeks of gestation. Otherwise, maternal antibody titers need to be monitored every two to four weeks, and ultrasonography performed to identify signs of fetal affection. At 20 weeks of gestation, fetal blood sampling (FBS) is carried out to determine fetal blood group, haematocrit, DCT, reticulocyte count and bilirubin. The finding of anti-Kell antibodies in an antenatal screening blood test is an indication for early referral to a specialist service for assessment, management and treatment