b. Laboratory Investigation of Suspected Hemolytic Disease of Newborns.
(1) A clotted sample of cord blood, and maternal blood should be obtained.
The mother's blood should be tested for: (1) ABO group, (2) RhO(D) type, and DU if
RhO(D) negative, (3) unexpected RBC antibody, and (4) identification of antibody if
results of detection test are positive. The infant's blood should undergo the following
tests: (1) ABO group, (2) RhO(D) type and D U if RhO(D) is negative, (3) direct
antiglobulin test, (4) elution if results of direct antiglobulin test are positive, and (5)
identification of antibody in the eluate.
(2) Because alloantibodies present in cord serum are lgG antibodies of
maternal origin, the ABO group of the baby is based entirely on cell grouping. If the
newborn has received repeated intrauterine transfusions of group O Rh-negative,
packed, RBCs, spurious results may be found in ABO grouping, Rh-typing, and in the
direct antiglobulin test.
(3) It may be particularly difficult to perform Rh-typing accurately in patients
with HDN. Several additional phenomenon may be present in patients with HDN and
cause false reactions in Rh-typing. False-positive reactions may occur because of:
(1) the presence of Wharton's jelly in incompletely washed RBC samples, and (2)
coating of Rh-negative red cells by an antibody other than anti RhO(D), for example,
(4) Enhancement of agglutination of these situations may be caused by
potentiators added to the slide or rapid tube test anti-RhO(D) serum. The use of an
albumin control or saline anti-RhO(D) serum will aid in detecting this anomaly.
(5) False negative or very weak positive Rh-typing is occasionally
encountered when the newborn is Rh-positive and the red blood celIs saturated with
maternal anti-RhO(D) so that all of the RhO(D) antigen sites are blocked ("blocked D").
This condition should be suspected when the mother is Rh-negative and the results of
the baby's direct antiglobulin test are strongly positive.
(6) The results of a direct antiglobulin test are usually strongly positive in
RhO and "other" HDN, while they are usually weakly positive or negative in ABO-HDN.
Identification of antibody in the eluate of cord cells should be done whenever the results
of the direct antiglobulin test are positive. If the mother's serum is ABO-incompatible
with the baby's cells and doesn't have any unexpected antibodies, the eluate should be
tested against adult A1, B, and O cells by saline and antiglobulin techniques. The
procedure must be used to diagnose ABO-HDN. If the results of the direct antiglobulin
test are positive and an antibody cannot be demonstrated in the mother's serum or in an
eluate from the cord blood, suspect HDN resulting from a private or low-incidence
factor. This can be confirmed by testing the mother's serum with the father's RBCs, if
mother and father are ABO-compatible. If they are ABO-incompatible, the mother's
serum should be repeatedly absorbed at 4C and 37C utilizing a random cell of the