Being “Kell positive” signifies the presence of a specific protein, known as the K (or KEL1) antigen, on the surface of an individual’s red blood cells. This characteristic is an inherited trait, passed down through genes from parents.
The Kell Blood Group System
The Kell blood group system is one of several classification systems for human blood, similar to the more commonly known ABO and Rh systems. This system comprises numerous antigens, which are protein markers found on red blood cells. The KEL gene, located on chromosome 7, encodes these antigens, including the two most common ones: K (KEL1) and k (KEL2 or Cellano).
Inheritance of Kell antigens follows an autosomal dominant pattern. The k antigen is more common than the K antigen. Approximately 91% of Caucasians and 98% of Black individuals are Kell negative (lacking the K antigen). Conversely, the K antigen is found in about 9% of Caucasians and 2% of Black individuals.
Kell Positivity and Blood Transfusions
Kell positivity holds significant implications for blood transfusions. If a person who is Kell-negative receives blood from a Kell-positive donor, their immune system may recognize the K antigen as foreign. This can lead to the formation of antibodies against the Kell antigen, a process called alloimmunization. Once these anti-Kell antibodies develop, subsequent exposure to Kell-positive blood can trigger a hemolytic transfusion reaction.
These reactions occur when recipient antibodies attack and destroy transfused Kell-positive red blood cells. Symptoms can include fever, chills, chest pain, and in severe cases, kidney failure or shock. Anti-K antibodies are considered highly immunogenic, making the Kell system the third most likely after ABO and Rh to cause immune reactions. To prevent these reactions, blood banks carefully cross-match donor and recipient blood to ensure compatibility.
Kell Positivity and Pregnancy
Kell positivity is important during pregnancy, particularly for Kell-negative mothers. If a Kell-negative mother has been exposed to Kell-positive blood, such as through a transfusion or a prior pregnancy, she might develop anti-Kell antibodies. These maternal antibodies, typically IgG class, can cross the placenta and target the red blood cells of a Kell-positive fetus.
This immune response can lead to Hemolytic Disease of the Fetus and Newborn (HDFN). Anti-Kell antibodies are unique because they can suppress the production of red blood cells in the fetus, not just destroy existing ones. Screening for Kell antibodies is a routine part of prenatal care. If detected, the pregnancy is closely monitored using methods like ultrasound and Doppler measurements of fetal blood flow to assess for signs of anemia. In severe cases, intrauterine blood transfusions may be performed to support the fetus.
Managing Kell Positivity
While being Kell positive does not typically cause any direct health issues for the individual, its significance arises in specific medical scenarios. It is advisable for Kell-positive individuals to inform healthcare providers of their status, especially before any planned transfusions, surgical procedures, or during pregnancy planning.
Carrying a medical alert card or bracelet indicating Kell status ensures this information is readily available to medical professionals in emergencies. This helps healthcare teams select compatible blood products and plan appropriate management, mitigating risks. Recognizing Kell positivity as a blood type characteristic, rather than a disease, helps individuals and their providers navigate medical decisions effectively.