Antibody Anti-JKa - What is it and how does one get it?!

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Besides the ABO and Rh blood systems, there are over 30 additional blood groups. These groups, of which the Kidd System is one example, are determined by the presence and absence of proteins and sugars on the red cell surface membrane, and inherited from our parents. In your situation, you did not inherit the JKa gene from either parent, and your red cells lack the JKa protein. In the U.S., approximately 23% of caucasians and 9% of African-Americans are JKa negative.

While the majority of donors/patients with anti-JKa are exposed by transfusion or pregnancy, "unknown" still ranks high on the etiology list. It is possible, though less likely, that you were exposed at birth (though neonates tend to not produce alloantibodies), came in contact with someones blood via minor trauma (childhood injury, etc.), or may have had an unrecognized miscarriage.

Anti-JKa has been associated with Hemolytic Disease of the Newborn, though the condition tends to be mild. These antibodies, however, are notorious for hemolytic transfusion reactions (HTR's), especially for Delayed HTR. I would recommend informing your physicians and close family members of the JKa antibody. Additionally, you may wish to keep a medic alert card in your wallet identifying you as having this alloantibody. JKa antibody titers commonly drop below detection levels over time. If exposed on a subsequent red cell transfusion, rapid production of anti-JKa could cause the above mentioned DHTR.

In general, do not be overly concerned. Antigen negative red cells are easily obtained if needed, and you should have minimal-to-no problems with future pregnancies.
If you have any questions, please contact the Medical Director of the blood collection facility that identified the antibody.

Good Luck

Medical Director - regional blood center