Use of Monoclonal Anti-A in the Determination of a Neonate’s ABO Phenotype

This article describes a male neonate whose red blood cells (RBCs) at birth grouped AB with monoclonal (mouse) reagents, but grouped B with polyclonal (human) reagents. The RBCs reacted weakly with monoclonal anti-A, although this reagent often reacts strongly with cells in the subgroups of A that are weaker than A2 (Asub). The neonate’s mother had group A RBCs that showed a mixed field agglutination with polyclonal anti-A that is characteristic of A3 cells. The infant’s erythrocytes were retested at age 4 months to see if the discrepancy still existed. Tests performed at that time included an expanded ABO grouping of the infant, his mother, and another sibling, as well as an adsorption/elution performed with the infant’s cells and polyclonal anti-A. Test results indicated that this infant is group AsubB, with cells that adsorb and elute polyclonal anti-A. His cells’ reactions with anti-A are weaker than is characteristic of A3B cells. His mother and sibling have group A blood, with reactions characteristic of A3 cells.