Blood bank lec: Hemolytic disease of the Fetus and Newborn (HDFN)

This is the destruction of the RBCs of a fetus and or neonate by antibodies produced by pregnant individual

hemolytic disease of the newborn and fetus

About 95% of cases of HDFN were caused by antibodies in the pregnant individual directed against what antigen?

Rh/D antigen

Why has HDFN caused by anti-D decreased since 1968?

introduction of Rh immune globulin (RhIG)

True or false. Rh(D) incompatibility is common, although other rBC incompatibilities have surpassed D in frequency at referral centers.

true

What is the etiology of HDFN? (2)

- antibodies of IgG class are transported across the placenta
- antibodies directed against antigen on fetal RBCs that were inherited from father

Is the firstborn that is Rh+ with an Rh- mother affected by HDFN? Explain.

No, first born is unaffected because parent hasn't been immunized

When do fetal RBCs enter maternal circulation?

during gestation and delivery when placenta separates from uterus

How does Rh HDFN occur? (3)

- D antigen inherited paternally and fetal cells immunize pregnant mom and stimulate production of anti-D
- once pregnant individual immunized to D antigen, later offspring who inherit D antigen will be affected
- maternal anti-D cross placenta and binds to fetal Rh-positive cells

Transplacental hemorrhage of fetal RBCs into the maternal circulation occurs in up to ______ of pregnant individuals during gestation. What percentage of transplacental hemorrhage is seen at delivery?

- 7%
- more than 50%

What can increase the risk of fetomaternal hemorrhage? (3)

- amniocentesis
- chorionic villus sampling
- trauma to abdomen

The ability of individuals to produce antibodies in response to antigenic exposure can vary depending on what?

complex genetic factors

When an Rh- person is transfused with 200mL of positive blood, what percentage of people form anti-D? What percentage of Rh-negative mothers form anti-D after Rh positive pregnancy with no RhIG?

1. 20%
2. 16%

What subclasses of IgG are more efficient in causing RBC hemolysis of fetal cells?

IgG1 and IgG3 (not IgG2 or IgG4)

When does IgG transport across the placenta take place during pregnancy? What do the subclasses of IgG affect?

- starts in second trimester
- severity of the hemolytic disease

What is the most antigenic RBC antigen? What antigens follow this?

1. D antigen
2. C, then E, then c

Other than Rh group, this is considered the most clinically significant in its ability to cause HDFN.

anti-Kell

What does it mean if anti-Kell is present on immature erythroid cells in bone marrow on fetal cells?

severe anemia due to destruction of peripheral cell and precursor cells

What antibodies most commonly cause HDFN? (8)

- anti-D
- anti-D+C
- anti-D+E
- anti-C
- anti-E
- anti-c
- anti-e
- anti-K

What antibodies rarely cause HDFN? (6)

- anti-fya
- anti-s
- anti-M
- anti-N
- anti-S
- anti-Jka

What antibodies never cause HDFN? (5)

- anti-lea
- anti-leb
- anti-I
- anti-IH
- anti-P1

When does hemolysis occur in HDFN?

when maternal IgG attaches to specific antigens of fetal RBCs

What does rate of fetal RBC destruction depend on? (3)

- antibody titer
- specificity
- number of RBC antigenic sites

The rate of RBC destruction after birth ___________ because no additional maternal antibody is entering the infant's circulation through the placenta.

decreases

Fetal RBC destruction and the resulting anemia stimulate what?

fetal bone marrow to produce RBCs at an accelerated rate

What is the effect of half life of maternal IgG on fetal red cells?

antibody binding and hemolysis of RBCs continue for several days to weeks post-deliver

Pathogenesis in HDFN: immature fetal RBCs (erythroblasts) are released into circulation. Hepatosplenomegaly results from extra medullary hematopoiesis.

erythroblastosis fetalis

Pathogenesis in HDFN: severe anemia and hypoproteinemia lead to development of high-output cardiac failure with generalized edema, effusions, and ascites

hydrops fetalis

RBC destruction releases hemoglobin which is metabolized to ________.

bilirubin

How is bilirubin transported across the placenta? (2)

- indirect bilirubin transported across placenta and conjugated in maternal liver to direct bilirubin
- pregnant individual excretes conjugated bilirubin

What happens to bilirubin in infants after birth?

immature newborn liver cannot adequately process unconjugated bilirubin

Moderate to severe hemolysis levels can cause bilirubin levels to reach 18-20 mg/dL which causes what in the infant?

permanent damage to parts of the brain

What is the recommended obstetric practice for diagnosis of HDFN? (2)

- perform type (ABO and Rh) and antibody screen at first prenatal visit
- previous pregnancies and their outcomes and prior transfusions

What is the methodology of the antibody screen of the pregnant mother?

detect clinically significant IgG alloantibodies that are reactive at 37C and in AHG phase

What happens if the antibody screen is reactive? (2)

- antibody identify is determined
- follow up testing will depend on antibody specificity and clinical significance

many Rh-negative pregnant women have weakly reactive anti-D in the _________ trimester.

third

Why is anti-D weakly reactive in the third trimester of Rh- mothers?

due to RhIg injection given at 28 weeks or after event that results in fetomaternal hemorrhage

How long does RhIG remain reactive in mother? What titer indicates active immunization? What titer is seen with RhIG?

1. remain reactive for 2+ months
2. 4 or higher
3. <4

If a pregnant individuals has anti-D and paternal parent is D-positive, an Rh phenotype can help determine what?

chance of infant being homozygous or heterozygous for D antigen

Paternal genotyping can be done by what more sensitive and precise method?

DNA methods

How do paternal phenotype and genotype help in HDFN? (2)

- guides further testing of pregnant individual
- counseling for potential treatment plants and complications of HDFN

If a pregnant individual has anti-D and the father is likely heterozygous for D antigen, what can be done to determine if the fetus has the gene for D antigen? (3)

- amniocentesis
- chorionic villous sapling
- performed as early as 10-12 weeks gestastion

Amniocentesis and chorionic villous testing be performed for the genes coding what? (9)

- c
- e
- C
- E
- K
- Fya
- Jka
- Jkb
- M

What is the relative concentration of antibodies capable of crossing the placenta and causing HDFN is determined by?

antibody titration

The antibody titration method must include what phase?

indirect antiglobulin phase using anti-IgG reagent

What is the antibody titration result expressed as?

reciprocal of titration endpoint or as titer score (1:6= 6)

True of false. The titration must be performed exactly the same way each time the patient's serum is tested.

TRUE (important)

How long is antibody titers incubated and at what phases? What samples are stored to run in tandem with other specimens?

- 60 min incubation at 37C and AHG
- first serum/plasma sample

A difference of _____ dilutions or a score of ______ is considered a significant antibody titer.

>2; 10

What test can be done at 16 weeks gestation when a titer is repeatedly at 32 or above? What does this test determine?

- color doppler imaging to asses middle cerebral artery peak systolic velocity (MCA-PSV)
- presence of fetal anemia

What test is done if titer is <32?

MCA-PSV repeated at 4 week intervals beginning at 16-20 weeks then 2to 4 weeks in third trimester

What procedure is rarely used on mothers to test for HDFN? What procedure is noninvasive and gives the same information as the uncommon one?

1. amniocentesis
2. MCA-PSV

The concentration of bilirubin pigment in the amniotic fluid measured by the ______________ procedure as pregnancy proceeds predicts worsening of the fetal hemolytic disease.

∆OD 450 nm

Intrauterine transfusion intervention becomes necessary under what conditions? (4)

- MCA-PSV indicates anemia
- fetal hydrops is noted on ultrasound examination
- fetal hemoglobin level is less than 10g/dL
- amniotic fluid ∆OD 450 nm results are high

What risks and benefits must be weighed and evaluated before doing an intrauterine transfusion? (3)

- infection
- premature labor
- trauma to placenta

How is intrauterine transfusion performed?

accessing fetal umbilical vein and injecting donor RBCs directly into vein

After delivery, the neonate can develop what issue with bilirubin?

hyperbilirubinemia of unconjugated bilirubin

Phototherapy at what wavelength is used to change unconjugated bilirubin to isomers which has what benefit?

1. 460 to 490nm
2. less lipophilic and less toxic to brain

What does the IVIG do when given to a pregnant person? (2)

- IVIG competes with pregnant persons antibodies for the FC receptors on the macrophages in infants spleen
- reduces amount of hemolysis

The use of whole blood or equivalent to replace the neonate's circulating blood

Exchange transfusion

Why are exchange transfusions rarely required?

due to advances in phototherapy and IVIG

What is exchange transfusion used primarily to remove?

high levels of unconjugated bilirubin

What are other advantages of exchange transfusion? (3)

- removal of part of circulating maternal antibody
- removal of sensitized RBCs
- replacement of incompatible RBCs with compatible RBCs

What hemoglobin levels in the newborn require transfusion? What hemoglobin level indicates severe anemia and hypoxia in the newborn?

1. levels below 10 g/dL
2. <7 g/dL

Cord blood sample correlates with hemoglobin levels during __________.

gestation

What serologic testing of cord blood is used to confirm HDFN and prepare possible transfusion? (4)

- ABO grouping (ABO antigens weak on newborns so weak reactions seen)
- Rh typing
- Direct Antiglobulin Test (DAT)
- elution

What blood considerations are needed for intrauterine and neonatal transfusions? (6)

- group O RBCs
- cytomegalovirus (CMV) negative
- irradiated units used to prevent TA-GVHD
- RBCs must be antigen-negative for respective antibodies of birthing parent
- blood units less than 7 days from collection of donor
- Hgb S negative

Why must blood for neonatal and intrauterine transfusions be Hgb S negative?

decrease oxygen tension in neonatal period can cause blood to sickle

Active immunization induced by RBC antigen can be prevented by the concurrent administration of the corresponding RBC antibody. This principle is used to prevent immunization to D antigen by use of this.

RHIG

How does RHIg work? (2)

- RHIG attaches to fetal Rh positive cells in maternal circulation
- antibody coated cells removed by macrophages in maternal spleen

When is antenatal RhIg given? What risk does it pose to fetus?

1. 28 weeks in third trimester
2. no risk to fetus (titer of 1 or 2 in pregnant moms)

Why is RhIG adminstered?

known risk of immunization during pregnancy

Rh-negative non immunized patients receive RhIg within what time frame after delivery of an Rh-positive infant?

72 hours

The regular-dose vial of RhIg in the US contains sufficient anti-D to protect against what volume of packed red cells and whole blood? (2)

- 15 ml of packed RBCs
- 30mL of whole blood

What test is used to determine the volume of fetal hemorrhage?

Kleihauer-Betke test

How many cells are counted to determine the percentage of fetal cells in the Kleihauer-Betke test?

2,000 cells

True or false. RhIG has a benefit on those who have been actively immunized and has formed anti-D

false, RhIg has no benefit on person who has formed anti-D

RhIg is not indicated for the birthing parent if the infant is found to be what type?

D-negative

This occurs when infants are A or B and there are group O moms. A reaction occurs during first pregnancy.

ABO HDFN

What antibody causes ABO HDFN?

potent anti-A,B

When is the prenatal screening for ABO HDFN done?

detection best done after birth (no correlation with IgG antibodies and fetal RBC destruction)

What is the postnatal diagnosis of ABO HDFN? (4)

- no single serologic test diagnosis for ABO HDFN
- collecting cord blood samples on all delivered infants recommended
- jaundice occurring 12-48 hours after brith
- DAT positive

When the pregnant individual is ABO-incompatible with the fetus (major incompatibility), the incidence of detectable fetomaternal hemorrhage is ____________.

decreased

What is the benefit/ influence of ABO group HDFN? (2)

- protect against Rh immunization
- hemolysis in patient's circulation of ABO-incompatible D-positive fetal RBCs happens before the D antigen can be recognized by patient's immune system