Lecture 11 - HDFN (main)

Define HDFN:

∙ Occurs when fetal RBCs are destroyed by maternal IgG antibodies ∙ The IgG antibodies cross the placenta and shorten red cell survival

Define HDF:

Premature red cell destruction results in disease varying from mild anemia to death in utero

Define HDN:

Red cell destruction results in anemia and elevated levels of bilirubin in a new born child

Kernicterus.

Around what week of gestation does maternal IgG's cross the placenta to provide Ab protection?

Week 12.

[From week 12 to birth is when HDFN is concern due to maternal IgG's being present in fetus and destroying fetal RBCs]

When can the mother undergo sensitization to fetal antigens?

Anytime fetal RBCs enter the mother's circulation

What Rh penotype of mother and child are indicitive of HDFN?

Rh-Negative Mother

Rh-Positive Child

Primary and Secondary Immune Response in HDFN

1. Rh-Neg woman is pregnant with Rh-Pos child

2. Rh-Pos cells from child enter mother blood stream

3. Woman becomes sensitized and maternal antibodies are formed to fight against Rh-Pos cells

4. In next pregnancy with a Rh-Positive child

Requirements for HDFN to occur:

∙ Mother must have developed an IgG antibody to the fetal RBC antigen

• [NO Lewis

Manifestation process of Hemolytic Disease of the Fetus HDF:

1. The mother is exposed to a foreign antigen on fetal RBCs during/after pregnancy or from a transfusion

2. IgG antibodies against that antigen are formed (plasma cells)

3. In a subsequent pregnancy

The Greatest Threat to the child during HDF is:

Cardiac Failure

[Due to uncompensated anemia]

Manifestation process of Hemolytic Disease of the Newborn HDN:

1. The mother is exposed to a foreign antigen on fetal RBCs during/after pregnancy or through transfusion

2. IgG antibodies against that antigen are formed (plasma cells)

3. In a subsequent pregnancy

What is the term for when infants with HDN has unconjugated bilirubin cross the blood-brain barrier that binds to CNS tissues and cause permanent brain damage:

Kernicterus

Premature births are often seen in:

HDN

What are the Three Classes of HDFN:

∙ RhD HDFN

∙ ABO HDFN

∙ Non-Anti-D Alloantibody- mediated HDFN

RhD HDFN Etiology:

∙ Anti-D is responsible for the most severe cases of HDFN

∙ Alloimmunization occurs during first pregnancy if baby is D-Positive but rarely results in clinical symptoms (Sensitization)

∙ Following antibody production

Which particular antibody is responsible for the most severe cases of HDFN?

Anti-D

[#1 cause of death in HDFN's]

ABO HDFN Etiology:

∙ Most common HDFN

∙ Most cases are subclinical and do not need treatment

∙ Mild RBC destruction due to: ▫ A or B substances in fetal tissues and secretions neutralize most maternal antibodies ▫ Reduced number of A

What ABO phenotypes of mother/child are most common in ABO HDFN?

Group O mothers pregnant with Group A infants

Unlike RhD

which type of HDFN can affect the FIRST pregnancy?

Non-Anti-D Alloantibody- mediated HDFN Etiology:

∙ Any IgG antibody is capable of causing HDFN if the fetal red cells possess antigens that the mother lacks

∙ Anti-c is the second most common cause of HDFN

can be in combination with anti-D

∙ Next is anti-K

∙ Mechanism of HDFN is identical to RhD

Kell antigens are unique because they are expressed on RBC precursors in:

∙ CFU-D [Colony-forming units-erythroid]

∙ BFU-E [Burst-forming units-erythroid]

When HDFN is due to Kell Antibodies it is much more severe because:

Kell Antibodies will target the precursor cells and lead to severe anemia

Initial visit testing:

• Type and Screen

• Antibody ID

• Antibody titration for IgG Abs

Antibody Titration:

∙ Used to predict severity of HDFN

∙ Original titer done early in pregnancy

∙ Repeated again at 16-22 weeks and then 4-6 week intervals after

∙ Previous specimens are frozen

∙ A two-dilution rise in titer is cause for concern

∙ Titers must be carried out in parallel at same time in order to minimize error

What kind of Ab Titration results would indicate that further monitoring needs to take place?

a Two-Dilution rise in Titer takes place between the original specimen and subsequent specimen.

What is the main caveat when performing Ab Titrations?

The most recent specimens MUST be done in parallel with the original specimens to minimize testing bias.

Amniocentesis is a technique for monitoring HDF because:

Measurement of bilirubin in amniotic fluid can help indicate level of red cell destruction.

How does a Doppler Ultrasonography monitor HDF?

∙ It measures blood velocity [Flow of child's blood]

∙ Rate is inversely proportional to Hemoglobin

∙ Faster during anemia

∙ When there is few RBCs

List 3 reasons why a Hospital will perform a post-natal workup:

1. Mother is Rh negative: ▫ Need to know if she will need second dose of Rhogam ▫ Need to know how much Rhogam

2. When HDN is suspected

3. Mother is Type O ▫ Need to know if child is type A and

What specimens can be used in Post-Partum Testing?

∙ Cord blood collected at birth [Plasma or Serum]

∙ Specimen from mother if not enough sample from child

∙ Stored for 7 Days

Post-Natal test on Mother:

∙ Type & Screen [& Ab ID if present]

∙ If mom is RhD-Negative then you test the child

Post-Natal test on Baby to prevent RhD HDFN:

∙ Type & Screen then a DAT ∙ If child is RhD-Neg you still must perform a Weak D test ∙ If child is Weak D negative

Whats special Post-Natal test is performed on the mother if Mom is RhD negative and Child is RhD Positive?

Fetal Maternal Hemorrhage [AKA Rosette]

[Basically determines how much Rhogam is given to the mother]

What is the Goal of a FMH screen?

To determine if over 20 mL of RhD Positive fetal blood has spilled over into RhD Negative mother.

What is meant by a negative result of the FMH screen?

Means that the bleed did not exceed 20 mL.

The mother would then be issued One Unit of Rhogam since it is below the 30 mL mark

What does a positive result of the FMH screen indicate?

Means that greater than 20mL of blood had been spilled over and then Confirmatory test must be performed

Additional units of Rhogam are then given.

One unit of Rhogam covers how much bleeding volume?

30 mL whole blood bleed & 15 mL of RBCs bleed

What is the Fetal Maternal Hemorrhage confirmatory test?

Kleihauer-Betke Test

The Kleihauer-Betke test will:

∙ Quantify all fetal cells in mother's circulation via Acid Elution of a PB smear. ∙ Fetal RBCs will stain pink since HgbF is acid stable ∙ Maternal Cells will just wash away since HgbA is acid soluble

Hgb-F % in Cord Blood:

90%

Which Hgb type is Acid Stable in the Kleihauer-Betke Test?

Hgb-F

Hgb-F % in Adult Blood:

0.5%

Which Hgb type is Acid Soluble in the Kleihauer-Betke?

Hgb-A

Acid Elution of Hemoglobin types on PB smears:

∙ Hgb-F is Acid Stable

∙ Hgb-A is Acid Soluble

Gold Standard assay for FMH testing is:

Flow Cytometry

Testing on Infants with Suspected HDN:

∙ ABO/D only forward type

∙ Antibody Screen (can substitute mother plasma)

∙ If DAT is positive with IgG

What is the importance of DAT testing?

If infant RBCs are DAT positive

Do you need to use a polyspecific reagent when perform DAT testing on newborns for HDFN?

No

RhIG is given to _____________ Mothers.

RhD-Negative

When is RhIG given?

Before birth at 28 weeks gestation

&

Within 72 Hours of delivery

What is the main caveat of giving Rhogam?

∙ Only useful to RhD negative mothers who HAVE NOT been sensitized yet. *Mother must NOT have already formed an Anti-D alloantibody

Rhogam is given to RhD-Neg mother at any point that blood can cross over such as:

• Amniocentesis

• Abortion

• Abdominal trauma

Rhogam Dosage:

∙ 1 Dose for every 30 mL Whole Blood bleed / [15 mL of fetal red cells]

∙ If Bleed is 31 mL

What is the Time Limit for any RhD-negative woman who delivers a RhD positive infant to recieve Rhogam?

Within 72 hours of delivery

Why should there be no history of an Anti-D alloantibody in the mother when issuing Rhogam?

They are already sensitized and thus Rhogam will not be helpful at all so it is not given.

Would you give a RhD-Negative woman with no history of Anti-D alloantibody Rhogam?

Yes

In what situation would you perform Weak D testing on cord cells?

If mother is RhD-Negative and the child is RhD-Negative

Treatment of Hemolytic Disease of the Fetus:

∙ Cordocentesis

• Transfusion into the umbilical vein in utero

∙ In utero transfusion requirements*:

• O Negative

• Concentration (Hct 70-80%)

• Crossmatch compatible with maternal serum

• CMV Neg

• Hgb S Neg

• Irradiated

• Less than 7 days old

Phototherapy treatment of Hemolytic Disease of the Newborn:

∙ Sunlight [Mild Hyperbilirubinemia]:

• Child's skin exposed to direct sunlight

• Photo-oxidizes bilirubin

• Excreted in urine

∙ Bili-Bed [Mod. hyperbilirubinemia]:

• Exposure to Blue light

• Photoisomerizes bilirubin so it can be excreted without conjugation in the liver

• Excreted in the bile

Exhange Transfusion Requirements:

∙ Identical to the In utero requirements for fetus treatment

∙ BUT you can use ABO-compatible RBCs and AB FFP and use normal Hematocrit concentrations

Exchange Transfusion treatment for Hemolytic Disease of the Newborn:

∙ For SEVERE hyperbilirubinemia

∙ Removes whole blood from baby / Replace same volume with PRBCs

∙ Removes some bilirubin and antibody

∙ Much more aggressive and faster than phototherapy

∙ However, more dangerous

The younger and lighter a child is, the more sensitive the child is to:

Bilirubin levels