Lab testing should be carried out when an infant is born to an alloimmunized mother, and any time when HDFN is suspected later (ie cases of unexplained hyperbilirubinemia or anemia). “A rate of rise in bilirubin levels greater than 5 mg/dL/24 h (or >0.5 mg/dL/h) is suggestive of hemolysis in any infant; therefore, clinical jaundice (bilirubin >5 mg/dL needed to be clinically visible) in the first 24 hours strongly suggests a hemolytic process” 85.
Immediately after delivery, a cord blood sample should be obtained for such studies as fetal blood type, hematocrit and direct agglutination test (DAT). An Indirect Agglutination Test (IAT) or antigen phenotype may be considered in the case of maternal alloantibodies that have been shown to yield an affected infant despite a negative DAT. These include anti-C, anti-c, anti-Fya, anti-Good, anti-H, anti-Jra, anti-M, and anti-Mta antibodies. To read more about these exception antibodies see our additional reading by topic page.
Cord blood bilirubin and a complete blood count should be ordered including hemoglobin, hematocrit, neutrophil count, thrombocyte count and reticulocyte count. Even in the absence of a positive DAT/IAT result, it is advised to continue to monitor bilirubin in the infant every four to six hours for at least the first 24 hours of life. If bilirubin levels are higher than expected during the infant’s first week of life, repeat the DAT. Establish hemoglobin and hematocrit values at eight to twelve hours of age and until stable. Visible jaundice is a sign that the bilirubin level is rising, but it is a poor predictor of the concentration of bilirubin in circulation or in the brain – neonatal blood testing must occur. Visual assessments are not an acceptable way to monitor or treat an infant with HDFN.
It is important to note that in neonates who received IUTs in utero, the infant’s blood type and the state mandated newborn screenings may be incorrect due to the majority of the circulating red cells being derived from the donor blood used during intrauterine transfusions. Direct agglutination test (DAT) is often negative at birth in these infants as well.
During the first week of life, bilirubin should be checked daily, especially considering that bilirubin due to alloimmunization tends to peak at days four to six. Hemoglobin should be checked at least one additional time in the week after birth 44. Afterwards, weekly hematocrit and reticulocyte counts should be assessed and simple transfusions initiated if hemoglobin levels fall below 7 gm/dL or sooner if symptoms of anemia are present.
Bilirubin should continue to be checked at least one to two times a week until a steady decrease is certain. Current guidelines state that infants with hemolytic disease of the fetus and newborn are at medium or high risk for developing severe hyperbilirubinemia and its consequences “If phototherapy is used for infants with hemolytic diseases or is initiated early and discontinued before the infant is 3 to 4 days old, a follow-up bilirubin measurement within 24 hours after discharge is recommended.” 45 Home phototherapy is not an option for infants with HDFN and readmission may be necessary. In the case of infants who are readmitted for hyperbilirubinemia, a repeat TSB after subsequent discharge is an option 45.
Before discharge a follow up appointment should be scheduled with a pediatric hematologist or other provider. The discharging physician should alert the family pediatrician or pediatric hematologist of the follow up care plan. Pediatricians and parents should be aware that affected infants may develop significant anemia until 12 weeks of life, especially if they received IUTs during pregnancy (see Delayed Onset Anemia on Additional Reading by Topic page). Parents should be educated on the physical signs of anemia and when to return to the hospital if the infant deteriorates between appointments.
Elevated levels of circulating maternal antibodies in the neonatal circulation in conjunction with suppression of the fetal bone marrow production of red cells often results in the need for neonatal red cell “top-up” transfusions after discharge from the nursery. This results in a 1- to 3-month period in which up to 75% of these infants may need “top-up” red cell transfusions 96. Weekly reticulocyte counts and hematocrit levels should be assessed until a rising reticulocyte count is noted for at least 2 consecutive weeks. The threshold-for-transfusion includes a hematocrit value of less than 30% in the symptomatic infant or less than 20% in the asymptomatic infant have been suggested by some experts. Typically, only one neonatal transfusion is required, although a maximum of up to three has been reported.
For additional information on infant testing, see necessary laboratory assessments for infants exposed to maternal alloantibodies.