Clinical pathology selected abstracts

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Editor: Deborah Sesok-Pizzini, MD, MBA, chief medical officer, Labcorp Diagnostics, Burlington, NC, and adjunct professor, Department of Clinical Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia.

Retrospective analysis of hemolytic disease of the fetus and newborn caused by anti-M antibodies

July 2023—Hemolytic disease of the fetus and newborn is caused by maternal immunoglobulin G crossing the placenta and binding to fetal RBC antigens. In severe cases, it results in fetal or neonatal anemia, edema, hepatosplenomegaly, and death. In China, antibodies to the ABO blood group system are the most common cause of hemolytic disease of the fetus and newborn (HDFN) and account for 85.3 percent of cases. This is followed by antibodies to the Rh blood group system, which account for 14.6 percent of HDFN cases. Other blood group systems, including Duffy, Kidd, and MNS, may also cause HDFN. Few studies have investigated anti-M-induced HDFN (anti-M-HDFN), and most case reports in the literature are from Japan, India, Taiwan, and other Asian countries. The authors conducted a study to summarize laboratory findings and clinical features of HDFN. They retrospectively analyzed the data on 17 infants who were diagnosed with anti-M-HDFN between June 2013 and May 2019. The authors compared the maternal history, neonatal diagnosis on admission, and laboratory test results for those 17 infants with those of 15 infants who had HDFN involving the ABO blood group system (ABO-HDFN), 15 infants who had HDFN involving the Rh blood group system (anti-D-HDFN), and a control group of 15 premature infants. Anti-M antibodies are common, unexpected RBC antibodies, with IgM antibodies representing the majority and 50 to 80 percent of cases combined with IgG. The results of the study showed that in the anti-M-HDFN group, 94.12 percent, 35.29 percent, and 17.65 percent of infants had free antibodies in plasma, a positive direct antiglobulin test, and a positive elution test, respectively. In 12 infants, the free antibody reactions were stronger at 4°C than at 37°C, and the antibody titers at 4°C ranged from one to 512. However, the anti-M titers were not high in two severe cases. All 17 of the infants with anti-M-HDFN developed anemia requiring treatment, and one of them died. One neonatal death following treatment also occurred in the ABO-HDFN, anti-D-HDFN, and premature infant cohorts. The authors noted that of the 39 pregnancies in anti-M-HDFN women, seven resulted in stillbirth or neonatal death, which was significantly higher than for ABO-HDFN (zero of 35) and anti-D-HDFN (one of 41). These results are consistent with other studies. In addition, the authors noted that the study findings suggest that the incidence and severity of anti-M-HDFN may be underestimated and that anti-M may be a cause of unexplained stillbirth, neonatal death, and other complications. They also found that anti-M-HDFN was associated with younger gestational age, lower birth weights, and higher incidences of respiratory distress than were other HDFN types. The findings suggest that the anti-M-HDFN pathogenesis mechanism may differ from that of other HDFNs and that this requires further research. Furthermore, since a low anti-M titer may lead to stillbirth and severe fetal anemia, clinicians should follow pregnant women with anti-M antibodies closely.

He Y, Gao W, Li Y, et al. A single-center, retrospective analysis of 17 cases of hemolytic disease of the fetus and newborn caused by anti-M antibodies. Transfusion. 2023;63:494–506.

Correspondence: Dr. Qiushi Wang at wangqs18@vip.126.com