BLOODBANK SUPPLEMENTAL NOTES BY: NEKO, RMT

HEMOLYTIC DISEASE OF THE NEWBORN [HDN]

• Destruction of fetus/newborn RBCs by antibodies produced
by the mother
• IgG – the only antibody that can cross the placenta
• Fetus must possess an antigen that is not found in the
mother. This can be an antigen inherited from the father.

PREDICTION OF HDFN

PRENATAL/ANTEPARTUM TESTING
• Identify D-negative women who are candidates for RhIG
• Fetus is positive for an antigen and mother is negative for the • Identify women with antibodies capable of causing HDFN to
same antigen assess potential risk to fetus
• Develops in-utero • Should be performed in the first trimester and should
include ABO and D phenotyping
ABO HDN • According to AABB, testing the mother for weak D antigen is
• Most common cause of HDN but less severe compared to Rh NOT REQUIRED.
HDN
• Occurs in 1 in 150 births and can be treated with MATERNAL HISTORY
phototherapy • A woman with history of HDFN secondary to anti-D, a
• Occurs most frequently in group A or B babies born to group subsequent D-positive fetus has a much greater chance of
O mothers. being affected
▪ Group O has higher titers of IgG ABO antibodies • History of previously affected infant is useful in predicting the
compared with other ABO groups prognosis of future pregnancies
• Can occur in the first pregnancy (unlike HDFN caused by
anti-D) ANTIBODY TITRATION
• Helpful in making decisions when it comes to the
Rh HDN performance and timing of procedures such as:
• Mother is D negative while child is D positive ▪ Amniocentesis
• Most severe form of HDN ▪ Ultrasound
• Sensitization occurs very late in pregnancy = 1st child is NOT ▪ Color Doppler ultrasonography
affected ▪ Cordocentesis
• Baseline antibody titer should be determined during the first
trimester
▪ Spx should be frozen for future testing
o Testing previously frozen samples in
parallel with the current spx ensures
that any change in titer is not due to
technical variables/errors.
▪ Testing is repeated at 4-to-6-week intervals.
• Titer rising by two dilutions or greater is considered
significant

ULTRASOUND TECHNIQUES
• Color doppler ultrasonography
▪ Measures blood flow velocity
▪ Increased cardiac output and decreased blood
• Subsequent D-positive fetuses are affected viscosity are associated with fetal anemia
• In some cases, maternal anti-D binds to fetal D-positive • Peak systolic velocity in the middle cerebral artery of the fetus
RBCs and causes a positive DAT and minimal red cell is evaluated which is then used to determine the severity of
destruction fetal anemia without invasive procedures
• Severely affected D-positive infants can experience rapid red AMNIOCENTESIS AND CORDOCENTESIS
cell destruction and experience anemia in utero and develop • Cordocentesis – Sample is from the umbilical cord
jaundice within hours of delivery • Amniocentesis – assesses the status of fetus using amniotic
• Exchange transfusion may be necessary to reduce bilirubin fluid
levels and PREVENT KERNICTERUS after delivery ▪ Read at 350-700 nm and change of optical density
above the baseline of 450nm is a measure of
bilirubin pigments

BLOODBANK SUPPLEMENTAL NOTES BY: NEKO, RMT. [DO NOT SELL!]

 BLOODBANK SUPPLEMENTAL NOTES BY: NEKO, RMT
▪ Optical density is plotted on the Liley Graph
according to gestational age POSTPARTUM ADMINISTRATION OF RhIG
• Cord blood from infants born to D-negative mothers should
FETAL GENOTYPING be tested for D-antigen INCLUDING WEAK D [Weak D testing
• Molecular typing of fetal DNA using maternal plasma during is not required if the mother is the one being tested.]
second trimester • A non-immunized woman who delivers a D-positive infant
• Can assist in predicting the risk of HDFN should be given FULL DOSE of RhIg within 72 hours of
• Avoids amniocentesis and cordocentesis delivery.

POST-PARTUM TESTING DOSE

• Each vial of RhIg contains enough anti-D to protect against
FMH of 30mL
• 1 vial = 300 μg of anti-D administered intramuscularly or
intravenously
• Massive FMH requires more than 1 vial
• FMH is assessed using maternal sample and screened within
1 hour of delivery via rosette test.

ROSETTE TEST
• Screening test to quantify the number of fetal red cells
• < 1 rosette per 3 lpf = 1 dose of RhIG
• > 1 rosette per 3 lpf = quantitate bleed

RhIG
• Used to prevent HDFN
• Concentrate of IgG anti-D prepared from pools of human
plasma
• Given to D-negative women at 28 weeks of gestation
(Antepartum) and again within 72 hours of delivery
(postpartum) of a D-positive infant
• Should only be given to a D-negative woman that HAS NOT
YET PRODUCED anti-D

KLEIHAUER-BETKE
• Kleihauer-Betke or a flow cytometry is performed to calculate
the dose of RhIG
• Flow cytometry – measures fetal hemoglobin or D-positive
cells or both
• Kleihauer-Betke acid elution is based on the fact the fetal hgb
is resistant to acid elution and adult hgb is not.
▪ Fetal hgb – appears bright pink = retains their hgb
▪ Adult hgb – susceptible to acid = hgb leaches into
buffer and appears as ghost cells

ANTEPARTUM ADMINISTRATION OF RhIG

• Initial dose should be given to unsensitized D-negative
mothers at 28 weeks of gestation.
• Mothers should be D-negative and fetus should either be D-
positive or unknown.
• D-negative mothers that has been previously immunized to D
References:
is not a candidate for RhIG as well as D-positive mothers.
Blaney and Howard “Basic & Applied concepts of Blood banking and
• All women should be phenotyped for ABO and D antigens and transfusion practices”, “Modern Blood Banking & Transfusion
tested for alloantibodies during the first trimester. practices” by Harmening, & MTAP notes.

BLOODBANK SUPPLEMENTAL NOTES BY: NEKO, RMT. [DO NOT SELL!]