ABO hemolytic disease of the newborn occurs almost exclusively in infants of blood group A or B who are born to group O mothers. Although ABO incompatibility is common, its related hemolytic disease has been reported to be low. In this study, we aimed to investigate the rate of direct anti-globulin test (DAT) positivity and clinical events, such as hyperbilirubinemia or anemia in infants born to group O mothers.
Using the charge code for cord blood evaluation, we were able to identify all cord blood evaluations from January 1, 2006 - December 31, 2007, and then select out the ABO incompatible births from group O mothers. We then reviewed the electronic medical records for demographic, clinical and laboratory information. Clinical events (anemia, jaundice, hemolytic disease) were investigated only in babies born at 37 weeks or higher gestation. Chi-square tests were used to cross-tabulate clinical events, demographic parameters (gender, ethnicity), and laboratory parameters (AO versus BO incompatibility, DAT-positivity).
There were 10,891 live births during the two-year period and 1519 (14%) of these were ABO incompatible. ‘Black’ ethnicity was registered in 80% of these babies. AO and BO incompatibility comprised 57.8% and 42.2% of the cases, respectively. 5.3% of the cases had concomitant Rh incompatibility. DAT was positive in 16.7% of the cases: 13.8% weakly or 1+ positive, and 2.9% 2+ or 3+ positive. DAT was more commonly positive among BO-incompatible cases compared to AO-incompatible cases (21.7% versus 13.1%). Among blacks, DAT-positivity in BO incompatibility was more common (24.9% among blacks compared to 7.8% among non-blacks, p<0.001). Concomitant Rh incompatibility did not affect DAT positivity rate. Among AO-incompatible babies, DAT-positivity was more frequent among females (15.5% in females vs 10.8% in males, p=0.045).
1299 babies were born at term (3 37 weeks gestation).of these infants, hyperbilirubinemia (defined as indirect bilirubin 3 8 mg/dL) was detected in 17.3% of babies. This was significantly associated with DAT positivity (40.6% in DAT-positive cases vs 12.3% in DAT-negative cases, p<0.001) and BO incompatibility (p=0.001). Hemolytic anemia (defined as hematocrit £ 45% and reticulocyte count 3 250,000/mm3 in the first week of life) was noted in 3.4% of cases, and was significantly associated with DAT positivity (13.2% in DAT-positive cases vs 1.1% in DAT-negative cases, p<0.001); BO incompatibility (p=0.001); and black ethnicity (p=0.001).
Our study indicated that cord blood DAT was positive in 16.7% of ABO incompatible pregnancies. BO-incompatible cases were more likely to be DAT-positive in blacks. AO-incompatibility was more common among girls, consistent with earlier studies that had shown a stronger A antigen expression among female newborns. DAT-positive cases were more likely to develop hyperbilirubinemia or hemolytic anemia. In addition, black ethnicity and BO incompatibility conferred significantly increased risk of hemolytic anemia in our study. Despite this strong association, the sensitivity of the positive DAT was 41.3% for hyperbilirubinemia and 70.5% for hemolytic anemia in ABO incompatibility.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.