Alloimmunization disorders

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Alloimmunization disorders

• Steven R. Allen, MD
• Scott White Hosp Clinic
• Temple, TX

2
Educational objectives

• Review fetal neonatal consequences of
  alloimmunization disorders
• Update genetics of Rh blood group
• Discuss strategies for prevention of Rh
  alloimmunization
• Develop management strategies for
  alloimmunization disorders

3
Immune responsesAb against Ag from

• Autoimmunity
• Isoimmunity
• Alloimmunity
• Heteroimmunity

• Self
• MZ twin inbred strain
• another member, same species
• another species

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Alloimmunization Disorders

• Rhesus blood group
• Atypical blood groups
• Platelet

5
Rh alloimmunizationHistoric landmarks
1940 Rhesus similar human RBC Ag
(Landsteiner Weiner)
1992 RhD non-D cloned
1932 hemolysis assocd with hydrops (Diamond)
1963 IP trans (Liley)

1938 a-fetal Hgb Ab postulated (Darrow)
1961 AF bili predicts HDN severity (Liley)
1985 PUBS trans (Daffos)
1600s hydrops, jaundice unknown etiology
1967 RhIG
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Rh alloimmunizationHistoric landmarks
1940 Rhesus similar human RBC Ag
(Landsteiner Weiner)
A Success Story
1992 RhD non-D cloned
1932 hemolysis assocd with hydrops (Diamond)
1963 IP trans (Liley)

1938 a-fetal Hgb Ab postulated (Darrow)
1961 AF bili predicts HDN severity (Liley)
1985 PUBS trans (Daffos)
1600s hydrops, jaundice unknown etiology
1967 RhIG
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Rh genetics biochemistry

• Rh D and more
• 2 homologous structural genes on 1p36-p34, RHD
  (encoding D) RHCE (encoding CcEe polypeptides),
  with 92 sequence identity
• Alternative mRNA splicing of single gene produces
  CcEe Ag variability

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Rh genetics biochemistry

• Gene product 417 AA non-glycosylated hydrophobic
  transmembrane protein, expressed only on
  erythrocytes (unknown function, and no shared
  sequence homology with any other known protein)
• Other blood groups encoded on chromosome 1 and
  other chromsomes

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Rhesus blood group
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What is Du?

• Present in 0.2-1 of caucasians
• Prior Du designation has been changed to weak D
  positive
• Created by a variety of mutations in RhD gene
• Manage as if D positive

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Incidence of Rh negativity

a caucasian trait
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Development of Rh alloimmunization

• Rh neg mother
• Maternal exposure to Rh pos RBCs
• non-pregnant transfusion, including RBC
  contaminated plts or WBCs
• pregnant transplacental hemorrhage (dose
  dependent incidence follows)
• 75 overall
• 60 ? 0.1 mL (0.1 mL sufficient for
  alloimmunization)
• 0.25 gt 30 mL

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Maternal immune response D alloimmunization

• Primary
• weak
• IgM (IgG wks later)
• develops over 8 wks to 6 mos

• Secondary
• rapid response of IgG
• higher avidity than primary response

Maternal response modulated by ABO status ABO
incompatibility is protective (alloimmunization
risk decreased by 75)
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Risk of Rh alloimmunizationP0, Rh neg mom, Rh
pos fetus, ABO compatibleno RhIG


90 due to peripartum feto-maternal hemorrhage
15
Risk of Rh alloimmunizationP0, term preg, Rh
incompatible, ABO compatibleEffect of RhIG

0.1
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Mechanism of hemolytic disease of the newborn
(HDN)

• Fetal RBCs destroyed by mat ?-D (IgG)
• non-complement mediated
• ?-D coated RBCs adhere to macrophages, form
  rosettes, are trapped in spleen
• RBC membrane fragments removed, with RBC
  fragility lysis
• Fetal anemia

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Mechanism of hemolytic disease of the newborn
(HDN)cont

• Extramedullary erythropoiesis
• erythroblastosis
• hepatosplenomegaly
• hep dysfxn, including hypoproteinemia
• portal hypertension
• Hydrops

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Rh Immune Globulin

• 300 ?g dose neutralizes exposure risk of up to 30
  mL fetal blood if given within 72 h
• AABB recommends screen before each dose (to r/o
  greater exposure volume or prior
  alloimmunizaiton)
• t 1/2 24 dgenerally effective for 12 wk
  (if given _at_ 28 wks, 15-20 will have low titer _at_
  term)
• risk of viral infxn minimal (Hep C) to absent
  (HIV)

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Prevention of Rh AlloimmunizationACOG RhIG
recommendations (Level A)

• Rh neg women not Rh alloimmunized should receive
  RhIG
• At approx 28 wks (unless FOB Rh neg)
• Within 72 h of del of Rh pos infant
• After a 1st TM pregnancy loss
• After invasive procedures, such as amniocentesis

Prac Bull 4, 5/99
cost-effective
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Prevention of Rh AlloimmunizationACOG RhIG
recommendations (Level C)

• RhIG prophylaxis should be considered if a
  patient experiences
• threatened abortion
• 2nd or 3rd TM bleeding
• External cephalic version
• Abdominal trauma

Prac Bull 4, 5/99
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Advantage to Rh immunoglobulin admin after BTL?

• Some women later want a pregnancy
• Improves availability of blood if a transfusion
  ever needed

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Screening for Rh Alloimmunization

• 1st TM Rh IDC
• If Rh pos, no further testing indicated
• If Rh neg IDC neg, give RhIG at 28 wks (and rpt
  IDC per AABB recommendation)
• If Rh neg IDC pos, check titer serially, q
  2-4 wks (mgmt based in part on titer)

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Predictors of severity of HDN

• Rhesus genotype of father of baby
• History of HDN
• Maternal Ab titer
• Amniotic fluid spectrophotometric measurements
• Ultrasonographic findings
• MCA peak velocity
• hydrops
• Invasive fetal testing

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Rhesus genotype of father of baby

• Rh neg NO RISK - routine prenatal care
  (regardless of maternal ?-D titer)
• Rh positive
• Zygosity for D can be predicted based on CcEe
  phenotype or genotype, ethnicity, and number of
  prior D-positive offspring
• if homozygous (45), then fetus at risk
• if heterozygous (55), fetus has 50 chance of
  being vulnerable
• Assume Rh pos ( fetus at risk) if unable to
  confirm otherwise

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History of HDN

• Subsequent pregnancies generally have similar or
  gt degree of alloimmunization
• Risk of recurrent hydrops 90
• Hydrops generally recurs at similar or earlier
  (not later) gestational age
• Risk of hydrops in 1st affected pregnancy 10

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Maternal ?-D titer

• ?-D titer is a crude predictor
• Critical titer indicates the need for additional
  evaluation
• Critical titer generally 16
  (altho may vary, 8-32, between labs and by
  technique)

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Ultrasonography to assess for fetal anemia

• Hydrops is a late sign of significant anemia
• Doppler velocimetry predicts anemia - best
  studied in MCA
• peak velocity gt 1.5 MoM for gest age predicts
  anemia (sensitivity ? 86 false pos rate 12)

NEJM 20003429-14
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Invasive fetal testing

• Amniocentesis
• ?OD 450
• fetal Rhesus genotype
• Umbilical blood sampling
• reserved for those at risk for severe anemia
  (based on non-invasive testing)

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?OD 450 (correlates with bilirubin concentration)
Wavelength (nm)

OD
?OD 0.21
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Liley graph
Gest age (wks)
Potential for fetal death in 7-10 d
3
?OD 450
2
1
Low risk of significant anemia
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Limitations to ?OD 450interpretation

• Original Liley graph limited to gestational ages
  ? 28 wks
• Physiologic (nl) fetal bilirubin production peaks
  at 23-25 wks
• Poor correlation between ?OD 450 and fetal Hct lt
  28 wks
• Betamethasone may artifactually lower ?OD 450

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Fetal blood analysis

• Direct degree of anemia
• lowest normal Hct 30 (18 wks) to 33 (30 wks)
• hydrops rarely occurs above 15 Hct
• Indirect correlates of anemia
• reticulocyte count
• Direct Coombs titer

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In utero transfusion

• Rationale for therapy
• suppression of abnormal erythropoiesis
• improvement of O2 carrying capacity
• prevention of hydrops
• opportunity for pulmonary maturation
• Blood for transfusion
• O negative, compatible with mother
• washed, irradiated, CMV negative
• tightly packed (Hct approx 85)

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Intraperitoneal transfusion

• EGA gt18 wks
• RBCs absorbed into fetal circulation, 12 per day
• larger transfusion volumes allow longer intervals
  between transfusions
• generally replaced by IVT

35
Intravascular transfusion

• EGA gt 18 wks
• transfuse max of 30-50 mL/kg
• repeat at intervals based on fetal status, final
  Hct, and expected decline of Hct (1 per day)
• better results than IPT if anterior placenta or
  fetus hydropic

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Prognosis for survival following transfusion

• Intraperitoneal
• 9 (if transfusion required before 25 wks) to
• 49 (includes hydropic fetuses) to
• 84 (best reported)

• Intravascular
• 82 (hydropic) to
• 89 (non-hydropic) to
• 96 (best reported)

?
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Suppression of Alloimmunization

• Not effective
• Promethazine
• Oral Rh RBC membranes
• RhIG

• Limited/potential benefit
• Plamsapheresis
• IVIG
• begin 1st TM may delay need for invasive
  testing

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Predictors of severity of HDN

• Rhesus genotype of father of baby
• History of HDN
• Maternal Ab titer
• Amniotic fluid spectrophotometric measurements
• Ultrasonographic findings
• MCA peak velocity
• hydrops
• Invasive fetal testing

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Start here if prior hydrops paternal Rh
positive
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Case 1

• 28 yo P1001 (uncomplicated prior preg)
• Anti-D titer rising to 16 _at_ 16 wks
• Husband Rh pos (prior baby Rh pos recd rhogam
  _at_ 28 wks p/partum no hx of transfusion or
  other exposures)
• Amnio _at_ 24 wks fetus D pos (and delta OD450
  extrapolated to mid Zone 2 of Liley curve)

41
Liley graph
Gest age (wks)
3
?OD 450
2
1
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Case 2

• 21 P2022
• Anti-D titer 256 _at_ LOC, 30 wks
• Unmarried new partner unaware of Rhogam given
  for last preg/EAb
• FOB not available for testing

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Liley graph
Gest age (wks)
3
?OD 450
2
1
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Case 3

• 31 yo P3103
• Last pregnancy was delivered _at_ 34 wks for hydrops
  (neonatal demise from HDN)
• Current husband father of all her children one
  prior Rh neg child
• Anti-D titer?

45
Liley graph
Gest age (wks)
3
?OD 450
2
1
46
Atypical Blood Group Alloimmunization

• Accounts for 2-5 of HDN increasing as Rh
  alloimmunization becomes less common
• Develops after blood transfusion
• RBCs for transfusion compatible only for ABO D
• incidence of sensitization 2 after transfusion
• Incidence 2 in general Ob population

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Examples of atypical alloimmunization

• Fetal risk
• Kell (K)
• Duffy (Fya)
• Kidd (Jka)
• M
• S

• Benign
• Lewis (Le)
• I
• P
• Duffy (Fyb)

Extensive list - use reference chart
48
Management of Atypical Alloimmunization
(-)
()
(-)
( or unknown)
Kell suppresses erythropoeisis - greater
anemia PUBS sooner
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Neonatal alloimmune thrombocytopemia

• Typical presentation
• intracranial hemorrhage (10-30 of affected
  infants)
• 1st pregnancy commonly affected (50 of cases)
• 12 mortality
• Rare 1/1000-1/2000 incidence
• Recurrence 75-90 (same partner)

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Neonatal alloimmune thrombocytopemia

• Etiology
• Maternal IgG abs directed against fetal plt Ab
• ?-HPA-1a most common (HPA-1a present in 97 of
  population)

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Diagnosing NAT

• Neonatal thrombocytopenia
• Normal maternal platelet count no ITP
• Discordancy in maternal paternal platelet Ab
  types
• Confirmation of maternal plt Abs
• Population screening not practiced

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Management of NAT

• Ab titers not predictive of prognosis
• PUBS (x 2-3), 1st _at_ 24-26 wks
• Treatment options
• Plt transfusions - can use maternal (weekly!)
• IVIG, maternal administration - most consistently
  effective confirm with PUBS
• Hi dose steroids if IVIG ineffective
• PUBS near term - C/S if severe NAT