(3) There is an inverse relationship between the cord hemoglobin and
bilirubin. That is, infants who are more severely anemic tend to have higher bilirubin
levels; however, the clinical severity of HDN does not correlate as well with the bilirubin
as with the hemoglobin.
(4) The strength of the positive results of a direct antiglobulin test does not
correlate well with clinical severity. About half of all babies affected with HDN whose
results of a direct antiglobulin test are positive do not require exchange transfusion.
Nevertheless, the serologic tests on cord blood must be regarded as urgent procedures
so that the pediatrician may know as soon as possible whether the baby is at risk.
(5) The major risk to the baby in the first few hours is heart failure because
of severe anemia. Afterward, kernicterus or brain damage from hyperbilirubinemia is a
more frequent concern. Both of these complications may be prevented by exchange
transfusion. Sequential accurate hemoglobin and serum bilirubin determinations are of
major importance in the decision regarding when, and if, exchange transfusion is
c. Late Anemia. Occasionally, babies affected with HDN develop a significant
anemia at 3 to 5 weeks of age caused by their reduced hematopoietic activity and
continued hemolysis. Since the diagnosis of HDN may not be suspected, all anemic
infants in the first 3 months of life should have laboratory investigations carried out to
evaluate this possibility (see para 2-18, this section, on Laboratory investigation of HDN
during the neonatal period).
d. ABO-HEMOLYTIC DISEASE OF NEWBORN. Hemolytic disease caused by
ABO incompatibility has special features. It is important to separate ABO sensitization
from clinically significant ABO hemolytic disease. Anemia is often absent or minimal in
this mild hemolytic process. Jaundice may occur in the first 24 to 48 hours of life (later
than in Rh disease) and this usually first suggests the diagnosis. The hemolytic process
may be evaluated by examination of blood smears for an increased erythrocyte
sphering, reticulocytosis and increased numbers of nucleated RBCs. No tests are
available for the accurate prenatal prediction of ABC hemolytic disease. Since the
disease is usually mild and exchange transfusion is infrequently necessary, early
delivery is never indicated.
2-17. PRENATAL STUDIES
a. Red Blood Cell Typing and Serologic Studies.
(1) The objective of prenatal immunohematologic studies is to identify those
women at risk of having babies affected with HDN. Once identified, these women can
be followed in order to estimate the degree of involvement, to determine the optimal
time for delivery, to notify the blood bank before delivery in order that blood be available
for possible exchange transfusion, and to alert the pediatrician for the arrival of a
possibly affected newborn. An obstetrical and transfusion history should be included as
part of the first obstetrical visit. Relevant tests to be requested on the first visit include: