HDFN and RHIG

Question 1

What is a normal hgb for infants at birth?

Answer 1

16-18 g/dL

Question 2

What is a normal hgb for infants 4-8 weeks of age?

Answer 2

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.

Question 3

What type of antibodies can cause HDFN?

Answer 3

All IgG can cross placenta.
IgG1 and IgG3 are most efficient
IgG1 causes severe hemolysis
IgG2 is least efficient at crossing placenta

Question 4

Which antigens are not present at birth?

Answer 4

I, Lewis, P1 are not present so antibodies do not cause HDFN

Question 5

What mechanism causes hydrops fetalis

Answer 5

anemia > increase RBC production in Spleen and liver > hepatosplenomegaly >portal vein hypertension > liver makes less protein + high cardiac output = edema and effusions > heart failure

Question 6

Why don’t you see hyperbilirubinemia in the fetus with HDFN?

Answer 6

In the fetus, bilirubin is transported to mother’s liver to be conjugated and excreted.

Question 7

Why is kernectus a concern for newborns with HDFN?

Answer 7

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.

Question 8

When is a titer result clinically significant?

Answer 8

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

Question 9

What tests can be done on a amniocentesis?

Answer 9

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

Question 10

What gestation is IUT usually done?

Answer 10

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%

Question 11

What type of blood is used for IUT?

Answer 11

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.

Question 12

When is weak D required on infants?

Answer 12

Only when mother is Rh negative (RHIG)

Question 13

What is blocked D phenomena?

Answer 13

Babys RBC are heavily coated with antibody so they type as D negative. DAT will be positive.

Question 14

What causes positive DAT in infants?

Answer 14

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

Question 15

What is the goal of exchange transfusion?

Answer 15

correct anemia
removes mothers antibody
removes bilirubin - some bilirubin is in intravascular space so may increase of after exchange

Question 16

How do you calculate blood need for exchange transfusion?

Answer 16

usually do a 2 volume exchange with HCT of 50%

Volume of RBC unit x HCT of unit = Volume needed x HCT needed.

Question 17

What is most likely mechanism of how RHIG works?

Answer 17

RHIG given IM and adsorbed into lymphatic system with high concentration of B cells. May trick B cells into thinking antibody is already present.

Question 18

How long does passive anti-D due RHIG remain in blood?

Answer 18

about 3 months

Titer is usually less than 4 and 2+ reactions

Question 19

When is RHIG contraindicated?

Answer 19

In IgA deficient people. RHIG contains IgA so may cause anaphylactic reaction

Question 20

What is the RHIG dose?

Answer 20

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

Question 21

What is weak D test to detect FMH?

Answer 21

Weak D detects a small amount of D+ in mother’s circulation. Read micro for MF.
Not very sensitive

Question 22

What is rosette test for FMH?

Answer 22

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.

Question 23

What is kleinhaur betke test for FMH?

Answer 23

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

Question 24

What is the ELISA technique to detect FMH?

Answer 24

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

Question 25

How is flow cytometry used to detect FMH?

Answer 25

Detects D+ cells
Investigational test detects hgb F cells
Cells are tagged with labeled antibody and gated to measure

Question 26

What is a critical MCA-PSV?

Answer 26

1.5 x Multiples of the median indicates moderate or severe anemia