Transfusion medicine illustrated. Maternofetal transfusion detected by gel-based typing.

Abstract

At our center, ABO and Rh typing of all newborns is performed on umbilical cord blood samples with tube-based testing; gel testing is an ancillary strategy used to resolve weak agglutination and other problems. We present two infants with unusual results. The RBCs of Infant 1 were agglutinated, by use of tube testing, with reagent anti-B, but not with anti-A. With gel testing, a mixed-field reaction (two bands) was seen with reagent anti-B (left figure, Case A). The mother typed as group B. The RBCs of Infant 2 were strongly agglutinated with reagent anti-B, but only weakly with anti-A, by use of tube testing. With gel typing, a weak mixed-field reaction was seen with reagent anti-A (middle figure, Case B). The mother typed as group A. A Kleihauer-Betke (acid elution) smear of each specimen revealed the presence of adult RBCs (pale ghosts) in addition to fetal RBCs (bright pink) (right figure, Case 1, Kleihauer-Betke test). In Case 1, the proportion of maternal cells was 32 percent; in Case 2, 20 percent. Each infant's sample had been drawn by use of direct venipuncture into the umbilical cord. We concluded that the RBCs of fetus 1 were group O, with maternal B cells in the sample; the RBCs of fetus 2 were group B, with maternal A cells, both due to maternofetal transfusion. Gel agglutination is known to be more discriminatory than tube testing in the detection of dual populations of RBCs. Trafficking of RBCs occurs bidirectionally between fetal and maternal circulations. The implications of fetal-to-maternal transfusion include maternal alloimmunization and hemolytic disease of the newborn; the consequences of maternal-to-fetal transfusion are less well understood.