HDFN and RHIG Flashcards
What is a normal hgb for infants at birth?
16-18 g/dL
What is a normal hgb for infants 4-8 weeks of age?
9-11 g/dL
Decreased survival of fetal RBCs.
Hgb F releases less oxygen to the tissues than Hgb A.
Expansion of the blood volume due to rapid growth.
Decline in erythopoietin production.
What type of antibodies can cause HDFN?
All IgG can cross placenta.
IgG1 and IgG3 are most efficient
IgG1 causes severe hemolysis
IgG2 is least efficient at crossing placenta
Which antigens are not present at birth?
I, Lewis, P1 are not present so antibodies do not cause HDFN
What mechanism causes hydrops fetalis
anemia > increase RBC production in Spleen and liver > hepatosplenomegaly >portal vein hypertension > liver makes less protein + high cardiac output = edema and effusions > heart failure
Why don’t you see hyperbilirubinemia in the fetus with HDFN?
In the fetus, bilirubin is transported to mother’s liver to be conjugated and excreted.
Why is kernectus a concern for newborns with HDFN?
newborns have immature livers and can’t conjugate bilirubin to be excreted. Indirect bilirubin increases and crosses BBB. bilirubin > 25 is critical. Leads to poor feeding, cerebral palsy, seizures and death.
When is a titer result clinically significant?
a 2 tube or 4 fold increase is significant
>/= 16 or 32 is considered critical
except Anti-K; titers don’t correlate well with disease severity
What tests can be done on a amniocentesis?
Bilirubin is measured using spectrophotometer with change in absorbance at 450 nm and plotted on Liley graph
L/S (Lecithin:Sphingomyelin) ratio to determine fetal lung maturity
What gestation is IUT usually done?
As early as 16-18 weeks with PUBS
Usually at 24-26 weeks and repeated every 1-2 weeks until delivery. Fetus RBC production will be inhibited because anemia is corrected.
Done if HCT less 30%
What type of blood is used for IUT?
Compatible with mother and fetus and negative for antigen that antibody is directed to
Irradiated, CMV safe, fresh, Washed?, HgS negative, 85% HCT
Can use mother’s blood. Doesn’t need to be ABO compatible with fetus because baby lacks antibodies.
When is weak D required on infants?
Only when mother is Rh negative (RHIG)
What is blocked D phenomena?
Babys RBC are heavily coated with antibody so they type as D negative. DAT will be positive.
What causes positive DAT in infants?
ABO incompatible - may be negative
Positive ABS due to RHIG - can cross placenta
If mother’s ABS is negative - consider low frequency antigen, test eluate or moms plasma against fathers RBC’s
What is the goal of exchange transfusion?
correct anemia
removes mothers antibody
removes bilirubin - some bilirubin is in intravascular space so may increase of after exchange
How do you calculate blood need for exchange transfusion?
usually do a 2 volume exchange with HCT of 50%
Volume of RBC unit x HCT of unit = Volume needed x HCT needed.
What is most likely mechanism of how RHIG works?
RHIG given IM and adsorbed into lymphatic system with high concentration of B cells. May trick B cells into thinking antibody is already present.
How long does passive anti-D due RHIG remain in blood?
about 3 months
Titer is usually less than 4 and 2+ reactions
When is RHIG contraindicated?
In IgA deficient people. RHIG contains IgA so may cause anaphylactic reaction
What is the RHIG dose?
Standard = 300 mg that protects up to 30 ml of whole blood or 15 ml of packed cells
Micro dose = 50 mg that protects up to 5 ml of whole blood. Only used <12 weeks for ectopic pregnancy
What is weak D test to detect FMH?
Weak D detects a small amount of D+ in mother’s circulation. Read micro for MF.
Not very sensitive
What is rosette test for FMH?
Detects D positive cells in mother.
Anti-D binds to baby’s RBC, R2r indicator cells bind to bound anti-D forming rosett’s
Can be falsely positive if mother is weak D positive.
What is kleinhaur betke test for FMH?
Detects fetal hemoglobin (hgb F) present in mother’s blood.
Hgb F is stained with hematoxylin. Count the number of Fetal cells in 2000 adult cells
What is the ELISA technique to detect FMH?
Detects D+ cells with anti-D, conjugated anti human IgG is added with substrate. Enzyme reaction occurs and yellow color is measured.
Test is expensive but accurate
