Are Kidd (Jka) Antibodies Hemolytic?
Yes, Kidd (Jka) antibodies are clinically significant hemolytic antibodies that can cause both acute and delayed hemolytic transfusion reactions, as well as hemolytic disease of the newborn.
Hemolytic Potential in Transfusion Settings
Anti-Jka antibodies are notorious for causing clinically significant hemolysis in both transfusion and pregnancy settings. 1 The American Society of Hematology specifically identifies Kidd antibodies among those that "can result in clinically significant hemolysis" and significantly increase the risk for acute or delayed hemolytic transfusion reactions (HTRs). 1
Key Clinical Characteristics:
Delayed Hemolytic Transfusion Reactions (DHTRs): Anti-Jka is particularly notorious for causing DHTRs due to the strong anamnestic (memory) response these antibodies exhibit. 2 This means previously undetectable antibodies can rapidly increase after re-exposure to the antigen, causing hemolysis days after transfusion. 3
Acute Hemolytic Reactions: Anti-Jka can also cause immediate acute hemolytic transfusion reactions when incompatible blood is transfused. 2, 4
Detection Challenges: A critical pitfall is that anti-Jka antibodies are transient and may be undetectable by standard gel testing methods, yet still cause hemolytic reactions. 3 In one study, 17 recently transfused patients developed anti-Jka detectable only by solid-phase testing but not gel methods—of these, 6 had confirmed DHTRs and 3 had possible DHTRs. 3
Hemolytic Disease of the Newborn
Anti-Jka can cause hemolytic disease of the newborn (HDN), though this is generally mild. 2 However, severe and even fatal cases have been documented:
Most HDN cases due to anti-Jka or anti-Jkb are mild-to-moderate with favorable prognosis. 4, 5
Fatal cases have occurred, including a documented case of severe HDN due to anti-Jkb resulting in intractable seizures, acute renal failure, and death despite exchange transfusion and phototherapy. 4
Clinical manifestations can include severe jaundice (bilirubin >46 mg/dL), anemia, and positive direct Coombs test. 4
Clinical Management Implications
Extended antigen matching including Jka/Jkb should be considered to prevent alloimmunization and subsequent hemolytic reactions. 1 The ASH guidelines note that while Rh (C, E) and K matching is the strong recommendation, extended matching including Jka/Jkb "may provide further protection from alloimmunization." 1
Critical Pitfalls to Avoid:
Never assume a negative antibody screen rules out anti-Jka: The antibody may be present at levels undetectable by routine methods but still capable of causing hemolysis upon re-exposure. 3, 6
Monitor post-transfusion hemoglobin levels: DHTRs typically occur 3-7 days post-transfusion, presenting with falling hemoglobin, jaundice, weakness, and elevated bilirubin. 6
Preserve pre-transfusion samples for at least 3 weeks to allow retrospective antibody identification if DHTR occurs. 6