Severe hemolytic reaction due to anti-JK3.

A 35-year-old gravida 3, para 3 Filipino woman with a negative antibody screen, no prior history of transfusion, and no hemolytic disease of the newborn in her children suffered a massive postpartum hemorrhage requiring transfusion. A severe hemolytic transfusion reaction occurred 5 days after delivery. Subsequently, a panagglutinin on a routine antibody identification panel was identified as anti-Jk3. The patient's red blood cell phenotype was Jk(a-b-) and all of her children were Jk(a-b+), yet the antibody that formed reacted with equal strength against all Jk(a)- or Jk(b)-positive cells. The rare Jk(a-b-) phenotype is more common in Polynesians. Anti-Jk3, like other Kidd system antibodies, is difficult to detect because in vivo production may be absent between provocative episodes and because these antibodies often show weak in vitro reactions. The increasing numbers of Pacific Islanders in the United States could result in more frequent encounters with this rare phenotype. Increased awareness of ethnic variability in blood phenotypes and of the capricious nature of Kidd antibodies can help pathologists and technologists deal more effectively with these cases.