Describe the pathophysiology of HDN
- HDN / HDNB / HDFNB (F= foetus)
- jaundice: elevated (>300 uM) &/or rapid inc. (>8.5 uM/hr) serum bilirubin w/in 24hr or 14+ days post partum
- Positive DAT: maternal Ab bound on Bb’s RBC
- severe HDN -> kernicterus, hydrops fetalis
Which antibodies commonly cause HDN?
IgG Aby reactive @ IAT
- Anti-c, -K, ABO
- Rhesus, Kell, Duffy, MNS, Kidd, ABO
Summarise the serological testing required during the ante and post natal periods.
- Ante-: @ first trimester visit: ABO & Rh(D) typing & Ab screen
- Retest in 28 weeks for ABO & Rh(D) type and Ab screen if neg.
- Post-:
• Mum have ABO & Rh(D) and Ab screen (if not done already)
• Bb: if mum is Rh(D) neg or has CSig. Ab = do ABO/Rh(D) group, DAT, Hb, Bilirubin, elution studies on baby - IF DAT positive => Ab screen
What are the requirements for blood products used in intrauterine transfusions?
- <5 days old
- ABO/Rh compatible w/ mum & foetus OR O neg cells
- *K neg
- Ag neg to maternal Ab (not want to give blood that’ll lyse bc from mum’s Aby)
- CMV neg
- Irradiated
- HCT ≥70% (bc not want vol. overload)
- XM compatible w/ maternal or infant plasma
2 test for determining foetal anaemia is baby @ risk of HDN (e.g. bc baby K+)
- Quantification/titration
- Middle cerebral artrey (MCA) Doppler ultrasound:
• non-invasive
• Velocity of blood flow in MCA
• inc blood flow = anaemia
In which scenarios are CMV-negative blood products required for transfusion?
- CMV-seroneg
- at-risk patients:
• Transplant recipients
• immunosuppressive chemo
• intrauterine transfusion
• neonate
• preg. women
In which scenarios are irradiated blood products required for transfusion?
- HLA-matched transfusions
- Intrauterine transfusion
- Newborns
- Immunodeficiency
What are CMV-negative blood componenets
- negative to cytomegalovirus - carried from WBC
What is irradiated blood components & it’s purpose
- RBC, plts treated w/ 25-50 Gy y-radiation
- prevent transfusion-assoc graft-vs-host disease
• prevent proliferation of donor T-lymphocytes
Describe why it is important to differentiate anti-D+C and anti-G in the management of HDN.
- bc someone producing anit-G (OR anti-G +C) can receive Rh(D)Gg
- BUT someone producing anti-D + C is not bc already produce/have immune anti-D
- differentiate using G- or D- differnetiation
Describe how serological testing of the father is beneficial in management of HDN
- perform XM w/ maternal plasma & paternal RBC
- bc father may produce low incidence Ag => baby inherits => will sensitize mum
- consider when there’s HDN w/ pos DAT but neg Aby screen for mum & ABO compatibility b/w mum & baby
Treatment options for HDNB
- phototherapy
- Exchange transfusion: intrauterine
how can you determine if a person has acquired or immune anti-D?
- probs prophylactic if anti-D quant is low
- immune: if quant. is stable or rising
Differentiate Rh(c) HDN w/ Rh(D) HDN
- Rh(c): present similar to HDN to Rh(D) incompatibility
- note: there’s is no prophalactic anti-c
Describe the G Ag
- An Ag on Rh blood group
- Present on C & D Ag = C+ and/or D+
How can you distinguish if a person has Anti-G or instead has 2 Aby, anti-C + D?
- Anti-C + D: Anti-D stronger than Anti-C
* Anti-G: reaction to anti-C (D-C+ cells) stronger than anti-D (D+C- cells)
interpret Rh(c) quant with risk of HDN
<7.5: unlikely risk to HDN
7.5-20: moderate risk to HDN
>20: High risk to HDN
How does anti-K differ to anti-D HDN (features of Kell HDN)
- previous history not indicate severity
- poor correlation b/w Aby titre & disease severity
- haemolysis not a dominant feature ≠ elevated bilirubin
= anaemia from insuffiecient erythropoeisis due to dec production as anti-K binds to K Ag on erythroid progenitor cells
ABO HDN
- high titre of IgG in mum (can go through placenta)
- elevated bilirubin w/o significant anaemia in foetal RBC: bc baby;s ABO Ag not fully developed
- sensitised cells not lysed = DAT pos (not always)
- spherocytes
Describe the tests for foetomaternal haemorrhage
- Acid elution / Kleihauer / - Betke test: Expose blood film to acid = denatures HbA (adult) => stain intact HbF (foetus) w/ erythrosine / eosine
- Flow cytometry: detect D pos cells in maternal blood using Fluorescent-labelled anti-D Ab
what needs to be done if mum has anti-K Aby
- refer to specialist
- phenotype/genotype father
- > if father is K+ genotype baby’s DNA from maternal plasma
- > if baby is K+, do MCA doppler& perform intrauterine transfusion if necessary
