HDFN & RhIg Flashcards
HDFN
- maternal red cell antibodies (IgG) crss placenta and attach to fetal cells causing hemolysis
- anemia in fetu
- increase in erythropoiesis (Erythroblastosis fetalis)
- mild to severe depending on antibody identity and concentration
factors of maternal Ab production (5)
- amount of blood (0.5 mL vs 25 mL
- immunogenicity of antigen (D vs Fya)
- previous exposure (primary vs secondary)
- maternal immune response (responder vs. non-responder)
- ABO compatibility
severe cases of HDFN (in utero)
- profound anemia
- hepatosplenomegaly
- hypoproteinemia
- cardiovascular failure (heart enlarged bc decrease in RBC mass)
- “Hydrops fetalis” severe edema = infant dies in utero
severe cases of HDFN (postpartum)
- anemia
- hyperbilirubinemia
> unconjugated bilirubin increases = Kernicterus - hemolysis continues postpartum
kernicterus
brain damage
- unconjugated bilirubin crossed BBB
- cerebral palsy-like effect
why don’t we see jaundice in fetus?
bc bilirubin in amniotic ac ad mom is getting rid of it so jaundice only seen in newborn
these blood groups are not associated with HDFN
Lewis
P
I (babies = i)
most common blood group associated with HDFN
ABO
- mild or subclinical
- first pregnancy can be affected
- IgG ABO antibodies (anti-A,B)
disease at birth for ABO HDFN
- no anemia or mild
- no jaundice, but bilirubin increases
- spherocytes on smear
What is RhIg?
- human source anti-D
> acquired from pooled plasma with anti-D
> anion exchange column chromatography
> solvent detergent (destroys lipid enveloped viruses) and ultrafiltration steps (removes non-enveloped viruses)
> lyophilized
how is RhIg delivered?
intravenous (IV) or intramuscular (IM)
mechanism of action RhIg
used for prevention of anti-D production in pregnancy when given to Rh neg females
mechanism of RhIg is not fully understood but may involve inhibiting the adaptive immune system by: (3)
- masking epitope of D antigen
- increasing rate of removal of D pos infant cells by opsonization (removal by spleen)
- FcyRIIB receptor inhibition of B cells
who gets RhIg? and when?
- given to Rh neg females without active anti-D
- 28 weeks gestation (26-32 weeks)
> removes any Rh pos fetal cells that enter maternal circulation prior to delivery - <72 hrs post-delivery of Rh pos or wk D pos infant
> removes fetal cells from circulation at time of delivery - additional dose may be given throughout pregnancy (amniocentesis, trauma, incomplete/therapeutic abortion)
standard dose RhIg
- 300 ug
- 1-300 ug will clear: 30 mL whole blood; 15 mL packed cells
** additional vials may be needed depending on size of bleed **
prior to RhIg, what was the only treatment for jaundice babies?
phototherapy
RhIg effectiveness
- 15% of white women are Rh neg
- no RhIg given = anti-D production = 12-13%
- 1 dose postnatal = 1%
- 28 wk and postnatal dose = 0.1%
half-life of RhIg
23-26 days
- may be detected up to 8 weeks in patients following injection (passive anti-D) and can interfere with PRETRANSFUSION testing
T or F. RhIg is not effective when active anti-D is present
T! it’s a prevention strategy so if it’s made… can’t remove it
T or F. RhIg prevents antibody production to other blood group antigens
F! you can still make anti-c, -kell, etc.
does passive anti-D harm the fetus?
no because given at last few weeks of pregnancy so risk is low and titre goes down eventually
other uses of RhIg
- Rh incompatible transfusions
> may be given to Rh neg females of child-bearing potential <45y who received Rh pos blood (emergency, error, Rh pos platelets) - treatment for idiopathic thrombocytopenic purpura (ITP)
> given to non-splenectomized Rh pos patients as an alternative to IVIg
prenatal testing follow up when antibody screen is positive
- Ab ID with panel
- perform titration
- antigen type mother and father
- verbal report to physician: antibody screen, ID, and titre
T or F. Level of Ab titre may not correspond to disease severity in infant
T
even though mom has a high Ab titre of anti-D, fetus could still be Rh neg
This titre is significant for IgG antibodies
titre of 16 or greater
any ttre of this blood group is significant
anti-K
- Kell can cause severe HDFN; on erythrobasts
What is considered a significant rise in titre?
greater than two tubes
- 8 to 32 is significant
- 8 to 16 is not
when do they check om’s Ab titre
month 7, 8, 9… etc.
physician decides what to do
could do amniocentesis to check bilirubin levels
what to do with a positive DAT?
elution
Elution
removes Abs for identification (panel)
dissociation
removes antibody for antigen typing
fetal bleed screen
- Rosette test
- detects if >30 mL Rh pos fetal cells entered maternal circulation
- formed on maternal sample taken 1 hr after delivery (when bleed happens)
- if mother is eligible for RhIg - FBS will be performed
- positive result means additional RhIg is required (NOT COMMON)
Kleihauer Betke test
- determines how much Rh pos blood has entered maternal circulation
- determines how many extra doses of RhIg is required
elution methods
- acid
- heat
- organic solvents
acid elution method
decreased pH will disrupt bonds between antigen and antibody
- add acid (pH 3) to elute antibodies from cells
- centrifuge and recover supernatant
- add buffer (pH 7) to supernatant restore pH
heat elution method
- dentatures protein structure of antigen so antibodies are released
- Landsteiner-Miller Heat 56C
- Lui-Freeze Thaw
organic solvents elution method
disrupts bonds betwen antigen and antibody by decreasing surface tension/dissolving lipid membrane
- Ether
- Xylene
- Dichoromethane
partial elution
- dissociation or cell-saving elution
- EDTA Glycine Acid (EGA) = destory Kell antigens
- Chloroquine diphosphate (CDP)
- ZZAP/WARM
> Papain = destroys MNS, Duffy, Chido & Rodgers
> DTT = destroys Kell - modified heat 45C
this test is performed on the mother’s postpartum sample to determine if > 30 mL of fetal blood has entered her circulation
Rosette test
how to perform a Rosette test
- maternal 3% suspension made
- incubate ^ with monoclonal anti-D at RT (binds to infant Rh cells)
- wash to remove unbound Abs
- indicator cells added = R2R2 cells that will bind to antibody-coated infant cells causing agglutination that can be detected MICROSCOPICALLY
- presence of agglutinates = significant amount of fetal cells in maternal circulation (>30 mL)
- follow-up testing for quantitation
T or F. Fetal cells are usually macrocytic
T
this test is performed to quantitate the number of fetal cells present in the maternal circulation
Kleihauer-Betke test
purpose of Kleihauer-Betke test
once size of bleed is determined, dose of RhIg can be calculated and administered to clear the fetal cells and prevent Ab formation
how to perform Kleihauer-Betke test
- PBS made from maternal postpartum sample and acid-treated
- fetal cells remain intact bc of high HbF; adult Hb = eluted from maternal cells
- slides are washed
- stained
- examined microscopically
- # of fetal cells (STAINED) are counted per number of maternal cells (ghost cells)> volume of bleed is calculated to determine how much additional RhIg is required
Number of (extra) vials of RhIg needed calculation
= [% fetal cells x maternal blood volume (~5000 mL)] / 30 mL (how much one vial can remove)
goal of an exchange transfusion
- reduce bilirubin level
- remove sensitized cells
- remove unbound maternal Ab
- correct infant anemia
blood product for an exchange transfusion
whole blood (red cells mixed with AB plasma) with a hematocrit of 0.55 (0.50 - 0.60)
exchange transfusion
small amount of baby’s blood (once born) is removed and replaced by donor whole blood
