Red Cell Isoimmunisation

Question 1

What kind of antibodies can cross the placenta and hurt the baby?

Answer 1

• auto-antibodies (mother has an autoimmune disease)
  
  • graves TSH-autoantibody or Hashimoto’s - hypo (not in utero but after born damage can be a problem) or hyperthyroid in fetus
  • CTD - SLE, scleroderma - dsDNA Ab - general FTT
  • ITP - immune thrombocytopenia purpura - most common - fetus thrombocytopenic
• maternal allo-antibodies = antigens that the mother doesn’t have
  
  • against 3 types of blood cells - red cells, white cells, platelets
  • perinatal allo-immune thrombocytopenia - intracranial and GI haemorrhage <5.
    
    • in adults - surgical bleeding <50by 10^9 per liter. mild thrombocytopenia
  • neutropenia
    
    • bacterial sepsis
      
      • treat with Ab and IVIG
    • only ex utero its a problem
  • red cell iso-immunization

Question 2

What type of antigens are on red cells?

Answer 2

• 3 groups of antigens:
  
  • Rhesus: C/c, D/d. E/e
  • Kell, Kidd, Duffy
  • MNS
• Harmless
  
  • ABO: A, B
  • Lewis - transfusions but not in fetus
  • P = IgM - doesn’t
• ‘Lewis lives, Kell Kills and Duffy dies’
• 85% are anti big-D, e and E - 1% of anti-red cell antibodies
• Fya = duffy A 1%

Question 3

Consequences of Red Cell Immunization? How can you predict severity?

Answer 3

• mild jaundice
• moderate (25%)
  
  • severe jaundice (can be fatal in brain)
• Severe
  
  • anaemic
  • fetal hydrops (generalised cardiac failure) - fetus oedema
  • FDIU - fetal death
• based on antibody titre (>500 = hydrops).

Question 4

What is the pathophysiology of iso-immunization of RBCs?

Answer 4

• Primary immunisation
  
  • blood transfusion
  • fetomaternal haemorrhage
    
    • bleeding = miscarriage, abortion, ectopic, APH
    • trauma CVS, amniocentesis, version, MVA
    • delivery
    • Occult (1% pregnancies) - prevented with prophylactic anti-D at 28 + 34 weeks. Prevent 90% of cases
• antibodes produced
• antibodies crosses placenta
• antibodies binds foetal antigen (only if they have it)
• consequences

Question 5

What is the Management of the standard patient for red cell immunization?

Answer 5

• first visit:
  
  • risk allocation (Ab titre)
  • father grouping
    
    • no antigen - normal risk
    • dd no risk
    • DD - all foetuses will have it - treat
    • Dd - 50% of foetuses will have it and requires fetal testing
      
      • amniocentesis (not CVS)
      • free fetal DNA from maternal blood
• Other visits:
  
  • low risk (<32 titre)
    
    • Ab titre every visit, at 38 weeks transfer maternal Ab
  • medium risk (64-256)
    
    • weekly US measurement of MCA (middle cerebral artery) velocity - increase flow in anaemia
    • CTG from 32 weeks - sawtooth
    • delivery at 38 weeks
  • high risk (>512)
    
    • US screening from 17 weeks
    • foetal blood sampling
    • intrauterine transfusion of foetal anaemia
      
      • mother’s blood type so mum’s RBCs wont attack
      • irradiated, volume titrate to response
      • peritoneal or into cord.

Question 6

What screening is performed for RBC iso-immunization?

Answer 6

• all pregnancies - screened for anti-red cell antibodies at first antenatal visit (1% negative)
• Rh negative women = 15% of population
  
  • screened additionally at 28 weeks
  • delivery
  • prophylactic anti-D

Question 7

What are the instances of primary immunization? What are some steps you can take?

Answer 7

• primary immunization
  
  • blood transfusion - compatible for ABO, Rh, <50 Kell negative blood (boys get Kell +) - women only get Kell negative blood (still get C/c, E, MNS).
    
    • RhD compatible
    • Kell - blood to women <50
    • others are too difficult
  • fetomaternal haemorrhage - passive anti-D - reduce risk of sensitisation to developing primary response.
    
    • bleeding in pregnancy
    • trauma
    • routine at 28 weeks and 36 weeks
    • post delivery
    • Kleihauer - big event measures Ab, done within 72 hrs. Already immunized contraindicated.
  • maternal to fetal haemorrhage?
    
    • <72 hrs of event
    • doesn’t help if already immunized.

Question 8

Why can’t you use family members for transfusion?

Answer 8

• can’t use related donors - donation under duress
  
  • might not say they have a blood borne virus
  • can still do it if they are already a donor though
  • screened - window period - takes a while to seroconvert. Got it recently

Question 9

What events make isoimmunization more likely? What interventions can you use?

Answer 9

• antenatal events
  
  • ECV
  • APH
  • traumatic delivery etc…
• compatible blood transfusion to mother
• anti-D not at the right dose
• IV drug user

Passive:

• Rh-+ antibiodies prioe to exposure
• within 72 hours of sensitising event (300micrograms IM for 15mils fetal RBCs)

Question 10

What happens if there is isoimmunisation?

Answer 10

• check maternal titre monthly
  
  • >1:16 - fortnightly MCA peak systolic volume
• genotyping of the paternal blood
  
  • homozygous or heterozygous.
• fetal DNA in maternal plasma (Brisbane)
  
  • similar to NIPT - check resus status for D.
  • can go around in amniocentesis (others have to do amnio, sensitise even more for Kell, C, Duffy etc…)
• check with US for fetal wellbeing (Multiple of the median)
  
  • intrauterine transfusion