A closely coordinated clinical approach is warranted among patients with hemolytic disease of the fetus and newborn (HDFN) in whom rare blood group antibodies are involved, according to findings from a review of two case studies published recently in the Journal of Perinatology.
In this study, the researchers focused on a 41-year-old and a 29-year-old pregnant patient, both of whom experienced alloimmunization against rare antibodies.
What is HDFN?
Hemolytic disease of the fetus and newborn (HDFN) is an immune-mediated red blood cell disorder that occurs when a baby’s RBCs break down quickly, which is called hemolysis. HDFN is caused by a mismatch between a mother’s and her baby’s blood type (A, B, AB, or O) or Rhesus (Rh) factor (Rh-positive or Rh-negative) during pregnancy.
A rise in bilirubin after a healthy delivery
The first case involved a 41-year-old woman who was pregnant for the third time. Her prenatal laboratory assessment did not reveal any abnormalities. An O-positive blood group typing with a negative antibody screen was reported.
Her pregnancy and delivery were considered uncomplicated, and she gave birth to a male infant.
Initially, no clinical issues were reported. The newborn’s hematocrit was 49%, which is considered within the normal range. Within 21 hours of delivery, however, the baby began to develop visible jaundice, and his bilirubin level rose to 18.6 mg/dL seven hours later.
Although phototherapy was initiated, his bilirubin level continued to rise. At 36 hours after birth, the newborn’s bilirubin level was 21.1 mg/dL and his hematocrit decreased to 40%.
Read more about the prognosis of HDFN
Infant discharged after testing positive for Cw blood group antigen
Because transfusion in the baby was being considered, blood bank serologic testing was performed, “which revealed an O-positive blood type and a negative antibody screen.”
Results of a direct antiglobulin test (DAT) were strongly reactive for immunoglobulin (IgG). Findings from an elution study, in which the eluate was tested against 14 reagent red blood cells (RBCs), revealed a specificity for the Cw blood group antigen, which is a “low prevalence member” of the Rhesus (Rh) blood group system.
The use of supportive care, including intensive phototherapy, was implemented. The infant’s bilirubin level began to decrease and his hematocrit stabilized. There was no need for him to receive a simple or an exchange transfusion.
The newborn was discharged home at five days old.
Blood transfusion required nationwide search
The next case described a woman experiencing her second pregnancy who delivered a term male neonate without any complications.
At one day old, the infant’s hemoglobin was 15.6 g/dL, which decreased to 13.1 g/dL on DOL 2. The baby’s bilirubin level was 13.7 mg/dL; his reticulocyte count was elevated at 8.3%.
At two days old, his bilirubin level rose to 19.9 mg/dL, prompting the initiation of intensive phototherapy. Based on blood bank testing, both mother and baby were O-positive and had strongly reactive antibody screens.
Results of antibody identification tests showed an immune response reactive with all reagent RBCs. The mother had a negative DAT; the newborn’s DAT was strongly reactive for IgG.
Tests revealed that the mother had developed anti-Ge3 against a high-prevalence blood group antigen. The infant required intensive phototherapy and a blood transfusion with Ge3-negative blood after a nationwide search. After treatment, the infant was stabilized and discharged.
Understanding low versus high-prevalence blood group antigens
Low-prevalence, also known as low-incidence, blood group antigens denote those that are reported in fewer than 1% of individuals in the general population.
The vast majority of the general population (more than 99%), however, will lack the low-prevalence antigen and thus be at an elevated risk for mounting an alloimmune response. The manifestation of an immune response to a low-incidence blood group antigen is a rare event, however, as is the occurrence of HDFN associated with these antibodies.
High-prevalence blood group antigens have typically been defined as those that exhibit a prevalence of greater than 99% in the general population. Certain antigens, however, may have a lower prevalence in specific patient populations.
According to the authors, “In these cases [in which] rare blood group antibodies are involved, a close collaborative partnership is required to ensure an optimal outcome for mothers and their neonates.”
