Q: I am a 51 years old female. I recently had an ankle surgery. I was cross typed and matched in case of blood transfusion. I just received a card in the mail from the hospital which states "Transfusion Restriction, This patient has the following clinically significant antibodies, Anti-Kell". What does this mean? I suffer from macrocytic anaemia but have had no transfusions for the last 11 years.

A:Our red blood cells (and some tissues) have got chemical substances called antigens on their surface and the ability to form these antigens is governed by genes inherited from parents. These antigens may be proteins, carbohydrates or other complex chemicals. The presence of these antigens (and their antibodies) has given rise to blood group systems and they play a role in blood transfusion and tissue typing. Currently about 30 different blood group systems are known in humans but the ones of clincal significance are the ABO system, Rh system, Kell, MNS, Lewis etc. The importance of blood group systems lies in transfusion and transplant medicine as we can receive blood (or organ) from only an individual whose blood group matches ours. In case of mismatch, the body's immune system recognises the 'foreign' antigen and fights it leading to disease states. Thus, blood group matching is done so that compatible blood (or tissue) is selected.

The Kell antigen system (or the Kell-Cellano system) was named after the family of the antibody producer Mrs. Kellacher. It is one of the major antigenic systems in human red blood cells and is important in transfusion medicine because the antibodies can cause severe reactions to transfusion of incompatible blood and hemolytic disease in newborn infants (HDN). It consists of over 20 different antigens (KEL1 to KEL24), which are coded by a gene complex present on chromosome 7. The k antigen (Cellano or K2) is far more common than K antigen (Kell or K1). Approximately 9% of the population has the K1 RBC phenotype and antibodies to K1 are developed in about 5% of persons receiving a single unit of incompatible blood. The reason is related to frequent transfusion-alloimmunization by Kell antigen and the low frequency of the K:1 gene among fathers. Kell hemolysis is severe in about half of cases.

Kell allo-immunization 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 hemolysis. Autoimmune hemolytic anemia (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 anemia. The majority of cases of Kell sensitization are secondary to incompatible red cell transfusions since blood is not routinely cross matched for the Kell antigen.

The K (K1) antigen is very immunogenic and causes strong reactions in case of mismatched blood transfusion and severe fetal anemia in sensitized mothers. It is produced only after exposure to the antigen as a result of pregnancy or repeated blood transfusions and thus the anti-K antibody is seen frequently in individuals. The k antigen (K2) too is immunogenic but as it is present in most individuals, the anti-k antibody is much less common.

You must be investigated for macrocytic anemia so that it is appropriately treated.