Clinical Significance:
• All IgG antibodies reactive by IAT 37 can cause HDFNB and HTR
• All antibodies reacting only at room temp or lower are not clinically significant
• Non significant antibodies may mask reactions of clinically significan antibodies.
• Crossmatch antigen – negative blood where possible
• Tx least incompatible blood if need is urgent
Effects of invivo antigen antibody reactions:
1. Reduced survival of transfused cells
2. Haemolytic transfusion reactions
a. Immediate - intravasacular haemolysis
b. Delayed - extravascular
3. Haemolytic disease of the fetus or newborn
4. AIHA
a. Warm
b. Cold
c. Drug induced
Factors affecting Clinical significance
• Clinical urgency of transfusion
• Thermal amplitude of antibody
• Antibody specificity and affinity
• Frequency of corresponding antigen
– Availability of compatible blood
• Antigen reactivity (e.g. dosage effect)
• Antibody concentration (titre) and avidity
• Immunoglobulin class / subclass
HDFNB Mechanisms and Prevention
Definition
Maternal IgG antibody crosses the placenta and reacts with foetal rbc antigen of paternal origin.
Varies from mild with very little or no effect to severe anaemia, oedema, hepato-splenomegaly in foetus or newborn
In utero:
Sensitisation of fetal cells with maternal antibody
Destruction of sensitised cells by fetal
Anaemia, cardiac failure, hydrops fetalis,
Bilirubin from Hb breakdown cleared by mother’s liver.
At birth:
Mild or no reactions
Anaemia, Hydrops
Hepato-splenomegaly
Maternal liver no longer available to clear bilirubin - Jaundice, Kernicterus,
Maternal immunisation
Previous transfusion or pregnancy
Crossing the placenta
Placental transport molecules on Fc portion of IgG react with Fc receptors on placental cells.
Prevention:
Transfusion policy for RhD neg young women
Immunoglobulin anti-D
Careful antenatal testing
Antibody monitoring,
Plasma exchange
Early delivery?
