A Case of the False-negative D Phenotype in a Neonate with a Strongly Positive Direct Antiglobin Test Rest

ABSTRACT

Accurate D antigen blood typing is needed owing to the clinical importance of the Rh blood group. We describe a female infant who was suspected to suffer from Rh incompatible hemolytic disease of the newborn, and who showed a strong positive direct antiglobin test (DAT) result and false red blood cell (RBC) agglutination in D typing. Using chloroquine dissociation of IgG, we confirmed that the antibodies coating her RBCs were of anti-D type. D typing with 0.8% RBC suspensions in saline using saline gel cards showed 2+ RBC agglutinations. After increasing the incubation time of dissociation by chloroquine for up to 4 hr, the dissociated RBCs began to show agglutination in both the tube technique (2+) and the gel card technique (4+) for D typing, although the DAT rest was still positive. Therefore, in order to prevent mistyping as a false-negative D blood group, whenever the D blood typing of a patient with a strong positive DAT rest does not show RBC agglutination, retesting of the D blood typing is recommended by using saline-suspended RBCs or dissociated RBCs.