HDN

different types of HDN

1. ABO

2. non-ABO (RH and other IgG antibodies)

necessary criteria for HDN to occur

1. mother exposed to antigen she lacks

2. exposure results in immunization and antibody production

3. antibody must be able to cross the placenta (IgG)

4. fetus must possess the corresponding antigen

how does HDN occur

• results from a maternal IgG antibody cross the placenta and attack the antigen the fetus possesses

• sensitization of fetal cells causes hemolysis → fetal anemia

• hemolysis releases bilirubin which cannot be cleared by immature fetal liver after delivery

what can elevated bilirubin levels cause

jaundice

what can happen to a newborn if elevated bilirubin levels are left untreated

can result in kernicterus (bilirubin depositing in the brain) → death

what is Rh HDN

occurs when Rh neg mom produces anti-D which crosses the placenta and sensitizes an Rh pos fetus

usually occurs after first pregnancy/exposure

Rh HDN severity

can become very severe in symptoms

ABO HDN

occurs in group O mom with group A or B fetus

can occur without prior exposure/pregnancies

ABO HDN severity

common type that is not severe in symptoms

other HDN

HDN which is not ABO/Rh in origin, but caused by some other IgG antibody directed against the fetal cells

other HDN severity

similar severity to Rh HDN

routine prenatal screening procedures

ABO/Rh and antibody screens

additional testing performed when a clinically significant antibody is found during prenatal screening

titering will be performed on the mom throughout the pregnancy to see if the antibody is gaining in strength and if the fetus will need intervention (transfusion or early delivery)

when is cord blood testing performed

is the mother is Rh neg or has a clinically significant IgG antibody

routine tests performed on cord blood

ABO/Rh typing and DAT on cord blood cells

can a reverse ABO type be performed on cord blood

no because the fetal immune system is underdeveloped and any antibodies present are of maternal origin

when can reverse typing be done on a child

around 4 months

why must cord blood be washed before testing

to remove Wharton’s jelly

how does wharton’s jelly interfere with cord blood testing

causes erroneous patient results due to pseudo-roleaux

what does DAT detect

in vivo sensitization of RBCs

what types of situations require a DAT

1. transfusion reactions

2. dx of HDN

3. dx of autoimmune or drug induced hemolytic anemias

what does an IAT detect

unexpected clinically significant antibodies

three phases in IAT test

1. immediate spin/room temp phase

2. 37C phase

3. AHG phase

procedures that use IAT test

1. antibody screen

2. crossmatch

what does a positive DAT indicate

coating of the RBCs with antigens (in vivo sensitization)

what must be done if the DAT is positive

an antibody ID must be done in order to provide blood that is antigen negative for the identified antibody

does a positive DAT indicate severity

does not indicate the severity of the HDN

purpose of elution

hemolyzes RBCs to elude the antibody attached to them

the eluate (eluded antibodies) are used in an ID panel to identify the antibody in the eluate

other lab tests performed on cord blood

1. cord hgb

2. cord bilirubin

indications of the presence/severity of HDN

how can Rh HDN be prevented

purified solution of anti-D injected into an Rh-neg pt within 72 hours after exposure to decrease the chances of developing an anti-D antibody

substance used to treat Rh HDN

Rh Immunoglobulin

RhoGam

how does RhoGam work

any Rh-positive cells in the Rh-negative pt will attach with the injected anti-D before they are able to stimulate the immune system to start making its own anti-D antibody

conditions where RhIg should be given to prevent HDN

1. Rh neg moms with no anti-D and an Rh positive/weak D positive newborn

2. after amniocentesis, cordocentesis, miscarriage, abortion

3. assumption of Rh positive fetus

how long after exposure can RhoGam be administered

administer within 72 hours after exposure

it takes at least 3 days for Rh negative immune system to recognize Rh positive RBCs in circulation

conditions where RhIg might fail

when the patient has already developed their own anti-D from prior exposure or inadequate dosage

fetal-maternal bleed/hemorrhage

when fetal blood has entered maternal circulation during birthing process

protection provided by one does of rhogam

30 ml of fetal maternal bleed (whole blood) or 15 mls of packed cells

when can rhogam be microdosed

works up until 12 weeks gestations because fetal RBC volume is less than 2.5 ml

steps necessary after a large fetal maternal bleed

more than one dose of rhogam may be required → fetal bleed screen and Kleihauer-Betke test needed

fetal bleed screen

semi-quantitative procedure where fetal cells present in maternal circulation will cause small clumps of agglutinated cells to be seen microscopically

what does a positive fetal bleed screen indicate

positive test indicates large fetal maternal bleed so more than one dose of rhogam is needed

Kleihauer-Betke test

quantitative test used to determine the amount of rhogam to administer based on the principle that fetal hgb and adult hgb will stain differently

after stain, fetal rbcs can be quantitated to calculate the number of rhogam doses to give

can too much rhogam hurt a patient

no because if there are no rh pos cells to attach to, it is simply cleared from circulation

blood requirements for an intrauterine or newborn exchange transfusion

1. <5-7 days old

2. anti-CMV neg

3. hgb S neg

4. negative for the antigen which corresponds to the maternal antibody

5. crossmatched with mother’s serum

6. irradiated to prevent GVHD

phototherapy treatment of HDN

ultraviolet light used to decrease jaundice by breaking down the bilirubin in newborn circulation