Blood groups classify blood based on antigens on red blood cells. The immune system develops antibodies in response to foreign antigens. The Kell blood group system is one such classification. Kell antibodies develop when an individual is exposed to Kell antigens their body does not naturally possess. This exposure most often happens through blood transfusions or during pregnancy.
Understanding the Kell Blood Group
The Kell blood group system involves antigens on red blood cells. K (KEL1) and k (KEL2, also called Cellano) are the most common. These antigens are part of the Kell protein, encoded by the KEL gene on chromosome 7. The K antigen is present in approximately 9% of Caucasians and 2% of Black individuals, while the k antigen is much more prevalent, found in about 91% of Caucasians and 98% of Black individuals.
Individuals develop Kell antibodies, which are irregular, when they encounter foreign Kell antigens. This most frequently occurs through blood transfusions with Kell-positive red blood cells if the recipient is Kell-negative. For example, about 1 in 10 Kell-negative individuals transfused with Kell-positive blood may develop anti-K antibodies. Pregnancy can also lead to the formation of these antibodies if a Kell-negative mother is carrying a Kell-positive fetus. These antibodies are predominantly of the IgG class and react at body temperature (37°C).
Impact on Pregnancy
The presence of Kell antibodies in a pregnant individual can have implications for the fetus, primarily Hemolytic Disease of the Fetus and Newborn (HDFN). This occurs when maternal Kell antibodies, which are IgG, cross the placenta and target the red blood cells of a Kell-positive fetus. These antibodies cause the destruction of fetal red blood cells, leading to anemia. Unlike some other blood group antibodies, anti-Kell antibodies can also suppress the production of red blood cells in the fetus by targeting red blood cell precursors, making the anemia more severe.
Monitoring pregnancies affected by Kell alloimmunization involves several steps. Antibody titers are assessed to gauge the level of antibodies in the mother’s blood, although a history of previous affected pregnancies may make titers less useful for predicting severity. Non-invasive prenatal testing, which analyzes cell-free fetal DNA from the mother’s blood, can determine if the fetus has the Kell antigen, confirming if the fetus is at risk. If the fetus is at risk, specialized ultrasound monitoring, specifically middle cerebral artery (MCA) Doppler scans, assesses blood flow in the fetal brain, which can indicate the presence and severity of fetal anemia.
If severe fetal anemia is detected, interventions such as intrauterine blood transfusions may be performed to deliver red blood cells directly to the fetus. In some cases, early delivery might be considered to prevent further complications. The management of Kell-HDFN often requires a multidisciplinary approach involving specialists in maternal-fetal medicine.
Considerations for Blood Transfusions
Having Kell antibodies is a consideration for future blood transfusions. If an individual with Kell antibodies receives blood that contains the corresponding Kell antigen, their immune system will recognize these foreign antigens and mount an attack, leading to a hemolytic transfusion reaction. These reactions involve the destruction of transfused red blood cells and can range from mild to severe, with anti-K antibodies known for causing severe reactions.
To prevent such reactions, laboratories perform cross-matching before any blood transfusion. This involves testing the recipient’s blood against the donor’s blood to ensure compatibility. For individuals with known Kell antibodies, Kell-negative blood must be provided for transfusion.
The cross-matching process includes screening for unexpected antibodies, such as Kell antibodies, in the recipient’s blood. If these irregular antibodies are detected, further specific testing identifies them. Only blood units confirmed negative for the specific Kell antigen will be released for transfusion, minimizing the risk of an immune reaction.