2014 65 Red Cell Antibodies Flashcards
When should blood group & antibody status be checked for all women?
Booking & 28/40
When & how should fetal genotyping be performed for red cell antigens?
- Non-invasive prenatal testing
- For C, c, D, E, e & K antigens
- When maternal antibodies present
- For other antigens, consider CVS or amnio if fetal anaemia a concern or if being performed for another reason
In the context of red cell antibodies, when should referral to a fetal medicine specialist be made?
- Rising antibody levels/titres
- Levels/titres above a certain threshold
- US features suggestive of fetal anaemia
- Hx of unexplained severe neonatal jaundice
- Hx of neonatal anaemia requiring transfusion or exchange transfusion
- Hx of previous significant HDFN
What thresholds for anti-D a) should prompt FMU referral, b) can cause severe HDFN?
a) >4
b) >15
What level of anti-c a) should be referred to FMU, b) can cause severe HDFN?
a) >7.5
b) >20
What level of anti-K a) should be referred to FMU, b) can cause severe HDFN?
All levels
What levels of anti-E should be referred to FMU?
All levels if anti-c also present
How often should red cell antibody levels be tested in pregnancy?
- Anti-c, anti-D & anti-K: every 4 weeks up to 28/40
Then every 2 weeks up to delivery - Other antibodies: at 28/40
Refer earlier if previous HDFN
How should pregnancies at risk of fetal anaemia be monitored?
- If fetus carries corresponding antigen for maternal antibody, and titre rises above specified level:
- Weekly USS, esp for MCA PSV
- FMU consideration of invasive treatment if MCA PSV > 1.5 MoM (multiples of the median) or other signs of fetal anaemia
What type of donor blood should be used for intrauterine transfusion?
- Group O (low titre haemolysin) or fetal ABO compatible
- Negative for antigen corresponding to maternal red cell antibodies
- Only in specialist FMU
How often should pregnant women with red cell antibodies & high risk of needing transfusion, eg placenta praevia or sickle cell, be cross-matched?
At least weekly
If maternal transfusion is required, what type of blood should be selected?
- Same ABO group
- Same RhD type
- K negative
4.CMV negative
Wat are the requirements to blood for intrauterine transfusion?
- Same as for neonatal exchange, except
- Plasma removed for increased haematocrit 0.7-0.85
- Always irradiated
What are the requirements of blood for neonatal exchange?
- ABO compatible with neonate & mother
- Rh D -ve, or identical to neonate
- K -ve
- Negative for antigens corresponding to maternal antibodies
- Less than 5 days old
- CMV -ve
- Irradiated unless delay unacceptable
- Plasma reduced, not in SAGM additive
- Hematocrit 0.5-0.6
What are the requirements of blood for neonatal top-up transfusion?
- As for exchange, except:
- Does not need to be irradiated, unless previous IUT
- Can be stored in SAGM
- Can be up to 35 days old
What cord blood investigations should be performed if mother has red cell antibodies?
- Direct antiglobulin test
- Hb
- Bilirubin
How should the neonate be managed in maternal red cell antibodies?
- Regular assessment of neurobehavioural state
- Watch for jaundice or anaemia
- Regular bilirubin & Hb
- Avoid early discharge
- Feed regularly to reduce dehydration & severity of jaundice
- Photo therapy &/or exchange transfusion for jaundice
What proportion of pregnancies have a) red cell antibodies detected, b) excluding anti-D & of clinical significance?
a) 1.2%
b) 0.4%
How do red cell antibodies come to be?
- Alloimmunisation
- From previous pregnancy, transfusion or transplantation
What is the pathophysiology of HDFN?
- Transplacental passage of maternal IgG
- Immune haemolysis of fetal/neonatal red cells
- Anaemia, jaundice
- Hydrops, preterm birth, perinatal death
What is the perinatal survival rate with red cell antibodies, a) overall, b) hydropic, c) non-hydropic?
a) 84%
b) 74%
c) 94%
At what stage of pregnancy can NIPT genotyping be done for red cell antibodies?
16/40
Except K, which is 20/40
What are the signs of fetal anaemia?
- Raised MCA peak systolic velocity, > 1.5 x MoM
- Polyhydramios
- Skin oedema
- Cardiomegaly
What is the difference between direct & indirect antiglobulin testing?
Direct: antibodies attached to surface of RBCs
To diagnose blood-related conditions eh autoimmune haemolytic anaemia
Indirect: antibodies floating in blood
To determine reaction to blood transfusion or sensitising event
Why is blood for exchange transfusions irradiated?
- To prevent replication of donor T leucocytes
- To prevent transfusion-related graft vs host disease
Why is SAGM additive not suitable for intrauterine transfusion or neonatal exchange transfusion?
Glucose can result in rebound hypoglycaemia
Mannitol can have diuretic & intracerebral pressure effects
When should delivery be timed for women with red cell antibodies that could cause fetal anaemia?
37-38/40
Earlier if titres rising or to time with IUT
What are the causes of neonatal a) perinatal & b) late anaemia?
a) passively acquired maternal antibodies
b) transient suppression of erythropoiesis, particularly after transfusion
Low numbers of erythrocytes despite low packed cell volume & normal erythropoietin
Why is sensorineural hearing loss increased in infants with haemolytic disease of the newborn?
Toxic effect of bilirubin on developing cranial nerve VIII
