Dear Dr. Roach: I was recently at the American Red Cross to donate blood and was given interesting material on the need for Black blood donors for sickle cell anemia patients. The booklet described how antigens work in red blood cells to improve patients’ health. I didn’t know until then that race can make a difference for blood donors with this specific disease.

How does the blood “boost” red blood cell production, if this is the correct verb? Is there a way other than informing donors who are already at Red Cross donor centers of the need for Black donors, such as announcements in Black-owned newspapers and magazines? I really found this fascinating as a longtime nonminority blood donor and welcome your thoughts. — J.B.

Answer: Most people know that there are blood groups, and you cannot donate blood from one person to another if their blood type is incompatible. For example, you can always donate blood from a person of one type (A, B, AB or O) to a person of the same type. Type O blood can be given to anybody, so people with this type are the universal donor. The RhD factor also determines the absolute ability to transfuse blood. Transfusion of RhD positive (often just called “Rh positive”) into a person who is RhD-negative will cause a severe transfusion reaction.

What is less-well known is that there are other antigens, especially RhC, E and K antigens that can also cause transfusion reactions, especially when a person has gotten many blood transfusions. This is frequently the case in people with sickle cell disease, the vast majority of whom have African ancestry. These transfusions initially make the transfused blood last for a shorter time than CEK-matched blood and may later cause more severe transfusion reactions.

About 85% of Black Americans have at least one of these antigens that differs from those typically found in white blood donors. Over 80% of regular blood donors are white.

Having matched blood type, not only for the major ABO and RhD factor, but also for the RhCEK factors reduces the likelihood that a person with sickle cell will become alloimmunized, meaning that it is very difficult to find blood they can accept without a transfusion reaction. Black blood donors are much more likely to have matching RhC, E and K factors, allowing the blood bank to provide the ideal blood for transfusion.

While any blood donor is welcome and prized, more Black donors are particularly needed, especially for recipients with sickle cell disease.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.