AlloimmunizationAlloimmunization When a person’s immune system develops antibodies against foreign antigens from the same species—such as when an Rh-negative mother’s body forms antibodies against her baby’s Rh-positive red blood cells. against the Kpa antigen, a rare protein found on red blood cells, may cause hemolytic disease of the fetus and newborn (HDFN), according to a review published in Hematology, Transfusion and Cell Therapy.
The Kpa antigen, which is one of 38 antigensAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. in the Kell blood groupBlood group A classification of blood based on inherited markers found on red blood cells. The ABO and Rh blood groups are most common in HDFN. system, has an estimated prevalence of less than 2% in white populations. Its prevalence in other racial and ethnic groups is extremely low, the authors state. The Kpb antigen, on the other hand, is found in over 99% of individuals.
SensitizationSensitization The process by which a mother’s immune system becomes “primed” to recognize and attack fetal red blood cells carrying incompatible antigens. to the Kpa antigen can occur as a result of blood transfusions, though alloimmunization during pregnancy is also possible in rare cases. This, in turn, may lead to severe anemiaAnemia A condition that occurs when the body doesn’t have enough healthy red blood cells to carry oxygen to its tissues. In HDFN, anemia occurs when maternal antibodies destroy fetal red blood cells. due to HDFN, though very few published cases exist in the literature.
A 2013 report, for example, describes a case of severe HDFN caused by the anti-Kpa antibodyAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens.. During imaging testing, the investigators observed hydrops fetalisHydrops fetalis A serious, sometimes fatal condition in which fluid builds up in a baby’s tissues and organs due to severe anemia from HDFN., a potentially life-threatening complication of HDFN. Blood testing confirmed the presence of the antibody. The child underwent several intrauterine transfusions, along with additional monitoring after birth.
Read more about HDFN causes and risk factors
The authors also reviewed evidence on testing for the anti-Kpa antibody in potentially-affected patients. While blood tests can often detect the antibody, genetic testing may also be used when serological testing is inconclusive. If an alloimmunized individual requires blood transfusions, the authors recommend using Kpa-negative blood units when possible.
“Alloimmunization, although rare, underlines the need to implement preventive strategies and accurate diagnosis to avoid hemolytic complications both in transfusions and in the perinatal context,” the researchers concluded. “This type of finding, although infrequent, highlights the relevance of detecting irregular antibodiesAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. in pregnant women.”
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