Haemolytic Disease of The Newborne Flashcards
Who is responsible for discovered the process behind HDN
Levine and Stetson
When did Levine and Stetson first suggest HDN
1939
What happens in HDN
(3)
Foetal/maternal blood group incompatibility
Maternal transfer of IgG antibodies against foetal rbc antigens
Results in haemolysis of foetal rbcs
How does the mother become sensitised against the foetus
(3)
Small amount of foetal blood enters mothers circulation during first pregnancy
Due to foetal bleed
igG cross the placenta
How is HDN treated
(3)
As long as the foetus gets to birth then the child can be treated -> from birth no more antibodies against foetal cells will enter circulation
Baby can die even after birth if there is no intervention
Photolight therapy is often used -> involves using UV light to treat haemolysis in babies -> breaks down bilirubin in jaundiced babies
What antibodies are responsible for HDN
Anti-D
Anti-c
Anti-K
What is the most common cause of HDN
Anti-D
When might there be immunisation against the foetal cells in the first pregnancy
(3)
Due to foetal cells entering the maternal circulation
Foetal maternal haemorrhage
But mother’s antibody titre is usually too low in the first pregnancy to affect the foetus
What blood do we give to women of child bearing years
D- and K- blood to prevent antibody formation prior to pregnancy
What is considered the danger period of HDN
Soon after the birth of a RhD positive baby
72 hours after birth
List the steps in HDN
(7)
Rh negative woman before pregnancy
Pregnancy with Rh-positive fetus
Placental separation
maternal sensitisation to Rh positive blood
Maternal development of anti-Rh antibodies
Anti-Rh antibody to foetal Rh-positive red blood cells
Haemolysis of foetal RBCs
What are the three steps to foetal rbcs destruction in HDN
(5)
Foetal rbcs are coated with antibodies
Coated rbcs are removed by splenic macrophages
Foetal haematopoietic tissues increase production of rbcs
Premature release of NRBCs from bone marrow
Severe anaemia with oedema
What are the other names for HDN
Erythroblastosis foetalis
Hydrops foetalis
Why is HDN also known as erythroblastosis foetalis
It results in the premature release of NRBCs from bone marrow
Why is HDN also known as hydrops foetalis
It causes oedema through leakage of fluid into extravascular spaces
What are the clinical effects of HDN on the foetus
(4)
Excess breakdown of Hb which leads to raised bilirubin
After birth mother’s circulation no longer removes bilirubin so it builds up in fatty tissue e.g. nervous tissue e.g brain -> kernicterus
Albumin which binds bilirubin is also low in newborns
Anaemia may result in organ failure if severe
What is kernicterus
Build up of bilirubin in the brain
Write a note on kernicterus
(6)
25-30% of affected foetus are born with pallor
Progressive jaundice ensues
Brain damage occurs within 3-4 days
Death occurs in 90% of patients via respiratory arrest
Surviving 10% have severe brain damage
This rarely happens in first world countries
Why does bilirubin target the brain
(4)
Brain composed of nervous tissue
Nerves insulated with myelin
Myelin is a fatty tissue
bilirubin has an affinity for fat
What happens when bilirubin binds to myelin of nerves
(3)
Bilirubin impregnates the myelin sheet
Nerve conduction is impaired -> results in short circuits -> nerves will short
Can cause cardiac arrest
What are prenatal tests
Test to identify women at risk of HDFN
What are the initial tests carried out on women at risk of HDFN
(5)
ABO/D test
Weak D test (optional)
Screening for IgG antibodies
Further igG antibody identification if screen positive
Antibody titration for IgG antibodies to establish baseline
What follow up tests are carried out on women at risk of HDFN is igG positive
Selected reagent red cell panel is run to exclude other clinically significant antibodies
Antibody titration in parallel with initial sample at 2-4 week intervals
What testing is carried out of pregnant women at 26-28 weeks pregnant
Confirm D typing -> can type foetus from mothers blood
What tests are done when a pregnant woman first visits the hospital
(3)
ABO and Rh group is checked
Antibody screening
Identifying antibodies as IgG or IgM
What tests are done when a pregnant woman is at 28 weeks
(4)
Titration/Quantification of Anti-D if present
Blood grouping of partner -> are they DD or Dd
Blood grouping of foetus
Amniocentesis to measure bilirubin of foetus
Chorionic villus sampling
What is chorionic villus sampling
(2)
Blood sample taken from chorionic villus to measure haemoglobin to see if foetus is suffering from anaemia
This is not really done anymore -> as there is a 1% chance of spontaneous abortion
How do we measure bilirubin of foetus now?
Use amniotic fluid
Use cell free foetal DNA
Doppler Ultrasound used now
What is the chorionic vililus
The region where the placenta binds to the foetus
what is cffDNA
Cell free foetal DNA
What does measuring cffDNA give us
(2)
We PCR the D- mother’s blood for RhD DNA
If RhD DNA present then it must be from the foetus therefore we can type the foetus as RhD+
What is a Doppler ultrasound
(2)
Colour Doppler ultrasonography
Used to detect foetal anaemia
How does Doppler ultrasound identify anaemia
Detects increased cardiac output and low blood viscosity
Severity of anaemia is determined by evaluating the peak systolic velocity in the middle cerebral artery
What is amniocentesis
(3)
Amniotic fluid is scanned spectrophotometrically for 350 to 700nm
A change in optical density (delta OD) above baseline (450nm) is a measure of bilirubin
The delta OD is plotted on a Liley Graph
How is a Liley graph used to pick up bilirubin
(3)
Upper zone (zone 3): indicates severe HDFN
Middle zone (zone 2): moderate disease
Lower zone (zone 1): mild disease
How is HDN prevented
(2)
Give mother anti-D antibodies before she can be stimulated to produce her own antibodies
When a D negative mother gives birth to a D positive baby she would be given these anti-D antibodies within 72 hours
Where do we get anti-D antibodies for transfusion from?
(3)
We haven’t been able to produce a monoclonal anti-D yet so instead we use a human blood product
They gave D positive blood to D negative men
Good responders who produced lots of anti-D antibodies were selected to donate plasma
When is anti-D given to pregnant women
Given at 28 weeks
Given in the 72 hours after birth
Why would we fail to prevent HDN
(5)
Anti-D not given
Anti-D not given in the 72 hours after birth of baby
Silent foetal maternal haemorrhage -> possibility that anti-D will run out by delivery
Incorrect timing of Routine antenatal anti-D prophylaxis (RAADP)
Another antigen causes HDN e.g. anti-Fy(a)
What is RAADP?
Routine antenatal anti-D prophylaxis
What is Routine antenatal anti-D prophylaxis (RAADP)?
Administration of RhD+ blood to RhD- pregnant women
What’s the one issue with RAADP
We can’t tell the difference between anti-D from mother or anti-D administered
Give the name of one of the anti-D products used regularly
Rhophylac
What Rh Igs are not indicated -> in what scenarios does anti-D not need to be administered
Patients who are already sensitised
Weak D’s
If the infant is Rh negative
For women not capable of child bearing age
What is FMH?
Foeto-maternal haemorrhage
List the methods for estimating FMH
(3)
Kleihauer Betke test
Rosetting technique
Flow cytometry
What is the Kleihauer Betke test
(2)
Kleihauer Betke acid elution technique
This test relies on the resistance of HbF to be eluted(removed) out of the rbc by an acid buffer solution
How is the Kleihauer Betke Test (KEB test) carried out?
(6)
Mothers blood with EDTA
Blood film
Dip in acid
Adult haemoglobin is acid soluble but HbF is not
Only foetal cells are left on the blood film
Count the foetal cells to determine how many cells are in mothers circulation and therefore how big of a bleed it was
What is the rosetting technique
(3)
A technique used to demonstrate small numbers of D positive cells in a predominantly D negative population
Detects FMH of approximately 10mls
This isn’t really carried out in Ireland anymore but is still done in the US
How is rosetting carried out
Count the rosettes seen in a blood film
D-positive cells will have rosettes of cells around them
How is flow cytometry used to estimate FMH
Use flourescein labelled anti-D antibody
What is a DAT
Direct Antiglobulin test
What is a direct antiglobulin test
(3)
DAT diagnoses the presence of antibodies on cells
Cells shouldn’t normally be coated in antibodies
There will be maternal antibodies on foetal cells if there has been a bleed -> these indicate that the rbcs are being destroyed
Why might there be antibodies on cells
(4)
Occurs in pregnancy
Occurs in autoimmune reaction
Occurs in transfusion
Used for demonstration of in vivo sensitisation of red cells with antibodies
How is a DAT carried out
(4)
Cells are coated with antibodies in vivo
We wash the cells to remove unbound globulins
We add anti-human globulin (AHG) which promotes agglutination after centrifugation
If there has been in vivo sensitisation then the cells will clump after addition of AHG
What is an indirect antiglobulin test
(3)
Serum with specific antibody mixed with reagent red cells
Washed 3x after incubation to remove unbound globulins
Anti-human globulin is added to promote agglutination on centrifugation
What is the direct antiglobulin test also called?
Direct Coombs test
How do we carry out a direct antiglobulin test
(4)
Blood sample taken from patient with haemolytic anaemia
Antibodies are shown attached to antigens on the RBC surface
The patients washed RBCs are incubated with antihuman antibodies (Coombs reagent)
RBCs agglutinate: antihuman antibodies form links between RBCs by binding to the human antibodies on the RBCs
How do we carry out an indirect coombs test/antiglobulin test
(5)
Recipient’s serum contains antibodies
Donors blood sample is added to the tube with serum
Recipient’s Ig’s that target the donors red blood cells form antibody-antigen complexes
Anti-human Ig’s are added to the solution
Agglutination of red blood cells occurs, because human Ig’s are attached to rbcs
How do we treat affected babies
(5)
We measure anti D and anti C to see how severe the disease is
Prenatal:
- Intra-uterine transfusions can be done
- Plasma exchange
Postnatal:
- exchange transfusions
- phototherapy to break down bilirubin pigment
What is considered mild, moderate and severe anti-D ?
mild < 4
Moderate = 4 -> 15
Severe = 15+
What is considered mild, moderate and severe anti c?
Mild = < 8
Moderate to severe = 8+
What is an intra-uterine transfusion
(5)
Transfusion guided by ultrasound via the placenta
Highly concentrated rbc pack is used
1 in 100 risk of spontaneous abortion
Transfuse about 20 units a year
Medical scientists will actually come out of the lab and see the patient for this
What is plasma exchange
This is done on the mother -> removes anti-D antibodies from mothers circulation
What tests may be done on a HDN baby
Haemoglobin
Bilirubin
DAT
How is Hb affected by HDN?
Babies born will have low Hb
How is bilirubin affected by HDN?
babies born will have raised bilirubin
What will a DAT reveal in HDN babies
May reveal babies have in vivo coating of red cells with maternal antibody
Why might an exchange transfusion be carried out on a baby
Take out some of the babies blood and give D negative blood -> only transfuse very small volumes approx 50mls
How do intrauterine transfusions work
Foetus receives transfusion through the umbilical vein in the placenta
What blood is given to newbornes in need of transfusion
(7)
Blood must be less than 5 days old
Must be packed red cells
Must be leucocyte depleted
Must be irradiated
Must be from a cytomegalovirus negative donor
Must be a small volume - approx 50 mls
Must be HbS negative
Why must blood be less than 5 days old to be given to a baby
(4)
Stored blood is fine for an adult
But rbcs leak potassium when in storage
High potassium can cause heart attack in newborns
New borns aren’t able to regulate salts and electrolytes as easy as adults
Why are rbc packs for babies leucocyte depleted
Leucocytes will continue to live in the patient if their body can’t kill them
Leucocytes will colonise baby’s circulation
Why are rbc packs irradiated
(2)
This ensures no nuclear material -> leukocytes can be found in the newborn
If this is not done Graft versus host disease will result which is nearly always fatal in newborns
What is graft versus host disease
(2)
White blood cells of the donor’s immune system which remain within the donated tissue recognize the recipient as foreign.
The white blood cells present within the transplanted tissue then attack the recipient’s body’s cells
What happens if a group O mother has a group A or B baby
(7)
Disease state usually mild
1st pregnancy can be affected -> already have anti-A or anti-B antibodies
Anti A or Anti B antibodies are IgG and can cross the placenta
Mild disease as ABO antigens are mildly expressed by the foetus
DAT will be positive
Phototherapy can be used to treat
Transfusion can be given if required
Why might a premature baby need a transfusion
(3)
Premature babies need a lot of monitoring so a lot of tests are carried out
Even though only small volumes of blood are taken this all adds up if baby is being tested multiple times a day
Baby might need a transfusion to top up
