Maternal ABO isohemagglutinins in infant circulation

We read with interest the recent study by Shaikh and Sloan in which they have investigated the clearance of maternal ABO isohemagglutinins from infant circulation. Because none of the infants, between 2 and 4 months of age, in their study was found to have maternal isohemagglutinins, they suggested that maternal anti-A and anti-B are cleared from infant circulation much earlier than other IgG antibodies. Thus, they concluded that infants who are at least 2 months old can safely receive ABO type– compatible RBC units without being tested for passively acquired maternal anti-A and/ or anti-B; in contrast AABB requires such testing in infants up to 4 months of age. The efforts undertaken by the authors to address this issue on the basis of evidence are appreciable; however, we feel that some issues, which have a bearing on the interpretation of the study, are still not clear. It is possible that a “measurement bias” introduced by selective testing for specific maternal isohemagglutinin could be the reason behind their findings. To elaborate, since the primary aim of the testing was transfusion, the group A infants were tested for only anti-A, group B only for anti-B, and group AB for both anti-A and anti-B. Because mothers’ blood types were not known, an infant population who might have maternal isohemagglutinin for which they were not tested (i.e., maternal anti-B in group A infants born to group A or group O mothers or maternal anti-A in group B infants born to group B or group O mothers) or infants in whom maternal antibodies were not expected, based on maternal blood group (infants born to group AB mothers), have been wrongly classified as infants in whom maternal antibodies had disappeared. This can be a considerable proportion of infants included in the study. Moreover, the infant population under consideration (infants >8 weeks of age) is underrepresented because they constituted only less than 10% of total infants in the study (their Figs. 1-3) and should be a cause of concern. To study the clearance of maternal isohemagglutinins from infants’ circulation, it would be prudent to test for both anti-A and anti-B if maternal blood group is not known or to select non-group O infants born to group O mothers’ and test for anti-A and anti-B serially. This can also possibly tell if infants’ blood type– specific maternal isohemagglutinin disappears earlier from the circulation due to binding to ABO antigens on RBCs and other tissues of infant. In the discussion, the authors mention that “Our current policy is to test infants under the age of 3 months for maternal isohemagglutinins. If the test is positive, the infant receives group O RBCs; if the test is negative, the infant receives type-specific RBCs. ” Does it mean that during the study period the authors were testing infants up to 4 months of age for maternal isohemagglutinins, as required by AABB, and have changed their policy subsequently to test infants only up to the age of 3 months, as a result of findings? On page 942, paragraph 1, which reads “Perhaps this clearance is enhanced by binding of anti-A and anti-B to B and A antigens, respectively, . Body” should be “Perhaps this clearance is enhanced by binding of anti-A and anti-B to A and B antigens, respectively, . Body. ” The editorial in the same issue addresses many of the other concerns and implications of change in the guidelines on the basis of this single study. To add, selective guidelines are known to result in error and introduction of age specific guidelines with such a narrow range are more likely to pose risk to infant than benefit. Finally, though, the results of this cohort study do not provide sufficient evidence to conclude that at 2 months, it is safe for infants to receive ABO type specific–compatible red blood cells (RBCs) without testing for maternal anti-A and anti-B; it certainly poses a relevant research question, which can be best answered by prospective longitudinal studies.