alloimmunisation Flashcards
Incidence of blood group antibodies
Incidence that is clinically significant
- 4% of woman have BG antibodies
0. 4% of these are clinically significant
Which blood group antigens result in severe Haemolytic disease
Occasional HDFN
Bad combination
No negative effect
Severe:
Anti D
Anti c moderate risk with 7.5-20
Anti K - refer once detected as severe anaemia can occur at 1:8
Sometimes Anti e, E anti Fya, anti Jka Anti S,s, deigo Anti E rarely causes anaemia Kell - Anti K, kpa, Kpb, Jsa Jsb ABO hydrops are very rare
Anti E and c are bad together
NO alloimmunisation
Lewis Le a/ b (IgM and not expressed on fetal RBC)
Duffy B - fy b
How does alloimmunisation occur
During pregnancy (miscarriage, ectopic, termination, invasive procedures, abdo trauma, ECV passive) delivery
Exposure to foreign antigens
Needle sharing and blood transfusions
What is the indirect coombs test
aim
purpose
stends
Indirect coombs test
AIM: detect plasma antibodies
Purpose:
pretransfusion testing
screen for antibodies affecting HDNB
Patients plasma + Red cells with known antigens + coombs reagent (antibodies against human antigens)
Agglutination = positive test
Use Indirect coombs test for pretransfusion testing and blood type cross matching
What is the direct coombs test
DAT
Aim
Detects antibodies or complement on the surface of RBC
Purpose autoimmune haemolytic anemia drug induced haemolysis HDNB Alloimmune hemolytic transfusion
method
add RBC from patient to coombs reagent
agglutination is positive
why is kell so bad?
and how to manage?
It both causes haemolysis and suppresses erythropoiesis by destroying the progenitor cells in the bone marrow
severe anaemia can be caused at low titres
not for titres
does have MCA PSV from 16 weeks
How many proteins in the Rh system?
What genes?
5 red cell proteins
C,c ,D, d, E
Rh negative is the absence of RhD
Ch 1 RHD and RHCE
How much blood is needed for Rh neg sensitization ?
0.1 ml blood
after an unmatched transfusion 50% of Rh neg will develop antibodies
What is the rate of ABO compatibility and the consequence?
Why is it not so bad?
If ABO is incompatible
2% alloimmunisation risk - risk less due to erythrocyte destruction before sensitization can occur
How to prevent Rh isoimmunisation
Anti D Recognise and treat sensitising events within 72 hours but value 9-10 days 6 weekly 9-% reduction in alloimmunisation Post partum prophylaxis - reduces risk to 1.5% per pregnancy
Antenatal prophylaxis - reduces risk 0.2% per pregnancy
How to manage anti D and cell saver
Reinfused blood can have fetal cells -
obtain a maternal blood sample 30-45 minutes after reinfusion to estimate the volume of fetal cells to dose adjust the anti D
What if birth is within 3 weeks of antenatal dose?
does she need post partum prophylaxis?
no unless she has an abruption
How to manage a woman with Rh neg blood group
Blood group antibody screen at booking and 28 weeks
Antenatal prophylaxis 28 + 34 weeks 625 IUI
Indicated prophylaxis
Can assess volume after sensitising event
Kleihauer, flow cytometry
Give additional anti D if needed
Directed prophylaxis in the Rh + neonate
When to give prophylaxis?
First trimester CVS Miscarriage Termination Ectopic Not enough evidence for threatened miscarriage before 12 weeks
Second and third trimester APH Amniocentesis. Cordocentesis ECV (successful or not) Abdo trauma or other suspective intrauterine bleeding
What is the initial work up if antibodies are found
Maternal antibody titres and quantification
Anti D, c, K monthly until 28 weeks then every 2 weeks
If other antibodies consider paternal testing
Fetal risk assessment
Fathers blood phenotype and genotype if certain of paternity
If father is Rh + but heterozygous 50% of children will be Rh neg
NIPT
Assess fetal genotype – if doesnt have Antigen then not at risk
Indicated if father is heterozygous
Amniocentesis and PCR of amniocytes
CVS is not used may worsen alloimmunisation and increased FMH
Maternal hx
Monitoring antibody
Quantitation is more reliable then titre
Referral 1:16/32 = 4-6 quant
Refer to MFM Hx of haemolytic disease High titres, abnormal USS Critical titre reached MCA PSV approaching / 1.5 MoM
How to monitor ongoing pregnancies
MCA PSV (peak systolic velocity)
Increased velocity due to increased cardiac output, vasodilation of the brain, decreased blood viscosity
Technique
Resting fetus
Circle of Willis imaged in axial image using colour doppler
Entire length of MCA
Close to origin of internal carotid artery
Gestation dependent
Measure from 18-20 weeks, to 36 weeks
Not as efficacious after 36 weeks
Levels <1.5Mom = 100% not anaemic
Measure 2 weekly
Levels >1.5 Mom = 65% anaemic 12% false +
Repeat in 24 hours – if the same then FBS +/- transfuse
After IUT MCA maybe unreliable
Liver length is a helpful adjunct
Assess for signs of hydrops
Ascites
Pericardial effusion, skin oedema, hydramnios
Hydrops required Hb 6 SD below normal level
If signs of hydrops then perform a cordocentesis with transfusion
What is the treatment if raised PSV?
treatment risks?
Treat anaemia IU transfusions 1% fetal loss rate per procedure Peritoneal vs placental cord insertion vs hepatic vein IPT - ? Interplacental transfusion Perform earlier gestations
Intravenous IUT
Survival 84%
70% if hydropic
95% if not
can be performed from 20 weeks up until 32 weeks
Balance how long to continue (when to pack it in and deliver)
Complications 1.2% PPROM, infection, EMLSCS, fetal loss
Ensure CMV free, irradiated 0 neg X matched cells, leukocyte deplete, packed hct 80 (prevent volume overload)
When
4 weeks earlier then previous pregnancy transfused
10 week prior to prev hydropic fetus / IUFD
As clinically indicated by USS
How much and how often AIm for hct 40-50% Hb over 120 Volume based on Hb and GA Can transfuse 1-2 weekly until erythropoesis is suppressed then 3-4 weekly
Maternal IVIG
High titre or early hydrops
Reduces titre and blocks placental antibody receptors
Delay need for transfusion
Notify blood bank
Consider weekly cross match if high risk maternal delivery
Cord bloods for bilirubin, Hb , DAT
What is the advice for future pregnancy
Anaemia occurs earlier in future pregnancies
consider sperm donor / surrogate
When does ABO incompatibility affect the fetus?
How common is it?
How can it be managed?
Incompatible for blood group A and B is the most common cause for haemolytic disease of the new born
20% of infants have incompatibility but only 5% are clinically affected
Often seen in first born
Most O woman have anti A and B from exposure to bacteria with similar antigens
Rarely progressive
Not an obstetric problems but a paediatric one – this is because
Antibodies are IgM and do not cross the placenta
Fetal red cells have fewer antigenic sites and thus are less immunogenic
No need to monitor antenatally
Monitor neonatal as hyperbilirubinaemia may need phototherapy or occasionally transfusion
What is the dosing for prophylaxis Rh Ig (RANZCOG)
first trimester 250 IU
If multiple pregnancy 625 IU
T2/3 625 IU
28/34 week prophylaxis 625 IU
Post natal - FHM quantified and Rh Ig given accordingly within 72 hours
