Alloimmunization 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 antigens in the Kell blood group 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.
Sensitization 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 anemia 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 antibody. During imaging testing, the investigators observed hydrops fetalis, 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 antibodies in pregnant women.”
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