HDFN + Baby Transfusions

Severe HDFN can be caused by:

Rh: Anti-D, -C, E, -e

Anti-K

Rh combos

Anti-Fya

Kidd: Anti Jka, -Jkb

Mild HDFN caused by:

ABO: Anti-A, -B, -A,B

Duffy: Anti-Fyb

What antibodies are not associated with HDFN?

IgM: Lewis, P1, I

What BGS are common for HDFN

ABO, Rh, Kell

Rare BGS for HDFN

Kidd, Duffy, MNSs

Where does RhIG come from

Human Source anti-D from pooled plasma (men exposed via transfusion, women exposed in pregnancy)

How is RhIG made

Plasma undergoes anion-exchange chromatography to adsorb anti-D. Solvent detergent destroys enveloped viruses, ultrafiltration removes non-enveloped viruses

How is RhIG transfused

After being lyophilized, can be given intravenously or intramuscularly

Purpose of RhiG

Prevent anti-D production of Rh neg mothers during pregnancy

Mechanism of RhIG

Anti-D can mask D epitope or increate rate of removal of D pos cells by opsonization

Hides D antigen before mom has chance to make antibodies

Non-pregnancy related uses of RhiG

- Given after Rh incompatible transfusions (mistake, emergency)

- Treatment of idiopathic thrombocytopenic purpura (ITP) in Rh pos non-splenectomized patients

How does RhiG treat ITP in Rh pos non-splenectomized patients

ITP = autoantibody against platelets, destroyed by spleen

Rh pos cells coated in RhIG, spleen preferentially destroys RBCs over platelets

Tests done on mom for pre-natal testing

ABORh, Antibody Screen

Tests done on baby for neonatal evaluation/workup for HDFN

ABO Rh with weak D testing, DAT (if mom Rh neg)

If mom's prenatal testing Ab screen is positive, what is follow up

Antibody ID with panel, perform titration of Antibody

Antigen mom and dad

Report to physician

When do Rh neg women receive prenatal injection of RhIG?

28 weeks (between 28-32)

When are additional doses of RhIg given during pregnancy

Extra given if Amniocentesis, Trauma (mom falls), incomplete/therapeutic abortion

Standard dose of RhIG

300 ug

How much volume of blood does 1 vial of RhIg clear?

30 mL whole blood, 15 mL packed cells

If Rh neg mom delivers Rh pos baby, when is RhIG given?

<72 hours after birth

Serological workup of HDFN on mom

ABORh. Antibody screen, Antibody ID if required

If mom is given postnatal RhIG, what other test must be performed?

Fetal bleed test (Rosette test)

Purpose of fetal bleed screen

determines if >30mL of fetal blood entered circulation

Theory of FBS

Add anti-D to mom's blood sample, anti-D will bind to baby cells after RT incubation. Wash away unbound anti-D and add R2R2 indicator cells that will bind to anti-D already bound to fetal cells = forms a rosette that is formed microscopically

When is FBS positive

If 5 rosettes are viewed per field in 5 fields

If FBS is positive, what test is performed after

Kleihauer Betke Test or Flow cytometry

Role of Kleihaurer Betke/Flow cytometry following positive FBS

Quantitate number of fetal cells in maternal circulation to allow for appropriate RhIG dosage

Theory of Kleihauer Betke test

Stain maternal blood smear with acid - elutes HbA out of RBCs to make ghost cells, but fetal HbF remains.

H&E counterstain is applied, and then fetal cells quantified using miller ocular lens. Fetal cells are bigger and brighter (macrocytes, fetal hemoglobin)

How to calculate number of RhIg vials needed

Number of vials = (% fetal cells x matenal blood volume) / 30mL. Always round up

2 burning questions that need to be answered in HDFN workup

1. Does mom need post-natal RhiG?

2. Is there a possibility of HDFN, and do we have to investigate?

If mom has pre-existing anti-D, is RhIG given?

No. No need

When is a DAT on a baby ordered?

When antibody is found on mother

If baby DAT is positive, what is next step?

Perform elution for antibody ID. If antibody ID is antibody from mom's pre-natal testing, antigen type baby

HDN caused by ABO

Occurs when mom is O blood, and baby is A, B, AB

Serological results for ABO HDFN on baby

DAT pos for IgG, but Ab screen negative

If mom is given 28 week RhIg and mom Ab screen positive in postnatal testing, do we get excited?

No, if antibody is Anti-D. This is passive. Mom can have EXM D neg blood if rquired

What is an intrauterine transfusion

Transusion while baby is still in utero. Catheter guided by doppler and ultrasound, inserted into umbilical vein

When is IUT performed

When HDN is occuring in utero (baby is anemic: large heart, tachycardic on ultrasound)

Blood product components for IUT

O neg, heavily packed cells

- CMV neg

- Irradiated

- Antigen negative for mothers Ab that causes HDFN

- Units crossmatched to mom plasma

Purpose of exchange transfusion

Occurs when HDFN known to occur: Reduces bilirubin, remove sensitized cells, remove maternal Ab, correct anemia

What is an exchange transfusion

When baby is born, small amount of baby blood removed, and replaced with donor whole blood (RBCs + Plasma)

Components of exchange transfusion blood

Group O Rh specific blood (Rh neg if HDN caused by anti-d)

- Blood < 5 days old (may be up to 7)

- Irradiated if IUT was performed

- Antigen negative to moms Abs causing HDFN, crossmatched to maternal plasma)