Blood Group: ABO

Common: Yes, especially among blacks. 53.6% of black type O people have anti-A

Causes HDN: Yes

Critical Titer: 1:16


One of the important things to note is that there is a difference in the severity of HDN based on race. HDN due to anti-A or anti-B is more severe in blacks and latinos than in whites [2, 3]. It is possible to have both anti-A and anti-B at the same time [7]. It is especially important that black infants are not discharged from the hospital prematurely and without proper follow up when ABO incompatibility is suspected. It has been suggested that a 6 hour bilirubin can determine the risk for significant hyperbilirubinemia (4 mg/dL) or severe HDN (6 mg/dL) due to ABO incompatibility [1].

ABO HDN remains the most frequent cause of severe and early jaundice in newborns [4]. Treatments include exchange transfusion and IVIG in addition to phototherapy. Exchange transfusion can lead to a 44.03% reduction in indirect bilirubin [6]. IVIG can reduce the need for exchange transfusion [4, 5]. One study suggests that maternal titers >1:512 can be good predictors of the need for IVIG and exchange transfusion [8], while another study says that titers aren’t useful in predicting the need for exchange transfusion [9].

In general HDN from Anti-B is viewed as being more severe than anti-A. This is because severe HDN due to anti-B is seen more frequently than severe HDN due to anti-A, however anti-A can cause severe HDN too. [10]. Another study said that anti-A and anti-B occur with almost the same frequency and there is no difference in severity [11].

In 4 of 11 cases of anti-A, the baby’s direct coombs test was negative, but the infant still affected. In the remaining 7 cases, the coombs test was weakly positive. In all 11 cases, the mother’s blood would destroy cells with A antigens in the lab. [12] This can be explained because there are less A antigen sites on infant cells than adult cells [13]. The reason the direct coombs test comes up negative when it should be positive is because of the lower level of antibodies sensitizing the cells [13].


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