Lecture 6 - Neonatal Testing

Question 1

what is HDFN?

Answer 1

haemolytic disease of the foetus and newborn

Question 2

how does HDFN occur?

Answer 2

when the mother has IgG antibodies in her blood that cross the plasma and bind to foetal red cells that possess the corresponding antigen

Question 3

what is hydrops fetalis?

Answer 3

heart failure in utero

Question 4

how can HDFN cause heart failure in utero?

Answer 4

the anaemia causes cardiac decompensation due to lack of red cells

Question 5

what is extramedullary erythropoiesis?

Answer 5

red cells being produced in an unusual location

Question 6

how can HDFN cause jaundice?

Answer 6

the removal of the erythrocyte antibody complex from foetal blood circulation causes haemaglobin degradation so causes increased unconjugated bilirubin levels

Question 7

how does bilirubin levels cause neurological damage? what is this called?

Answer 7

called kernicterus and it is caused by bilirubin accumulating in the grey matter of neurological tissue causing neurotoxic effects

Question 8

how is the neurotoxicity caused in kernicterus?

Answer 8

mass destruction of neurones via apoptosis and necrosis

Question 9

what are the symptoms of acute bilirubin encephalopathy?

Answer 9

legarthy, decreased feeding, hypotonia/hypertonia, high-pitched cry, fever, seizures or death

Question 10

what are the features of chronic bilirubin encephalopathy?

Answer 10

movement disorders, auditory dysfunction, oculomotor impairments, impaired digestive function, gastroesophageal reflex

Question 11

what is different in relation to HDFN with an IgG antibody and an anti-Kell antibody?

Answer 11

anti-kell can cause severe anaemia regardless of the strength of the antibody

Question 12

what are the effects of an anti-Kell antibody on red blood cells?

Answer 12

it suppresses the bone marrow so inhibits erythroid pregenitor cells, prevents formation of blood cells

Question 13

what are the microbiology antenatal tests?

Answer 13

HPB, HIV, syphilis

Question 14

what are the transfusion antenatal tests?

Answer 14

ABO group, antibody screening, ffDNA

Question 15

when do microbiology and transfusion tests occur?

Answer 15

8-12 weeks gestation

Question 16

what is the purpose of 28 week tests?

Answer 16

to confirm ABO and RhD group, for detection and identification of alloantibodies

Question 17

how is the genotype of the baby determined?

Answer 17

using PCR on free foetal DNA in the mothers circulation

Question 18

what is the ffDNA genotyping sensitive for?

Answer 18

RhD, C, c, E, e and Kell

Question 19

what concentration of anti-D levels cause referral to a foetal medicine specialist?

Answer 19

above 4IU/mL

Question 20

what concentration of anti-c causes referral to foetal medicine specialist?

Answer 20

above 7.5IU/mL

Question 21

what type of antibodies are quantified?

Answer 21

anti-D and anti-c

Question 22

how does quantification work?

Answer 22

amount of agglutination the antibody causes compared to the standard that runs at the same time

Question 23

what machine does quantification occur in?

Answer 23

continuous flow analyser

Question 24

what antibodies are used in titration?

Answer 24

anti-K, anti-E, anti-Fya

Question 25

how does the titration reaction occur?

Answer 25

serial dilutions of patient plasma are made and red cells added, the titre is the same as the highest dilution in which a reaction is found

Question 26

how does anti-D Ig injection work?

Answer 26

the injection coats the RhD antigens on any D+ foetal cells in the maternal circulation to mask them from the immune system to then be removed by the spleen

Question 27

what is RAADP?

Answer 27

routine antenatal anti-D prophylaxis

Question 28

how much RAADP is administered and when?

Answer 28

15000 IU at 28 weeks gestation

Question 29

what patients are given RAADP?

Answer 29

those who are RhD negative that have RhD positive baby

Question 30

what causes foeto-maternal haemorrhage?

Answer 30

foetal blood crosses maternal circulation

Question 31

how much FMH can the dosage of RAADP given protect against?

Answer 31

12mL for 1500IU

Question 32

when should as assessment of FMH occur?

Answer 32

following a sensitising event on a RhD negative woman, following delivery of RhD positive baby, following stillbirth/IUD on negative or positive women

Question 33

what is the acid equation method?

Answer 33

dry blood films are tied and immersed in an acid buffer, HbA is denatured and leaves behind blood ghosts, yet HbF are resistant and can be stained, therefore determines if HbF is present

Question 34

how does flow cytometry occur?

Answer 34

a fluorochrome conjugated IgG anti-D antibody reagent is used, passed through a laser so that the population of both types of haemoglobin can be identified and populations determined

Question 35

why cant flow cytometry be used on a RhD positive woman?

Answer 35

because an anti-D fluorochrome antibody is used

Question 36

when is suspected HDFN investigated?

Answer 36

when unexpected jaundice occurs, babies born to mothers with known alloantibodies

Question 37

how is HDFN investigated?

Answer 37

test for maternal antibodies, test for ABO incompatibility

Question 38

how is HDFN investigation performed?

Answer 38

ABO and RhD grouping performed on mother and baby samples, antibody screening panel and NAT on baby sample

Question 39

what blood group does a mother usually belong to when HDFN occurs?

Answer 39

usually a group O with a group A/B baby

Question 40

what is the doppler ultrasound?

Answer 40

determines the middle cerebral artery peak systolic velocity, which indicates the severity of the foetal anaemia

Question 41

what things indicate the need for foetal blood sampling?

Answer 41

severe anaemia before 24 weeks gestation, if there has been a post IUD, if there is an increase in maternal red cell alloantibody levels

Question 42

what is the purpose of IU transfusions?

Answer 42

prevent life threatening foetal anaemia and allow pregnancy to continue until the baby is viable

Question 43

how are IU transfusions adapted to lower the risk?

Answer 43

started as late as possible, and maximum safe volume with maximum haemocrit is given to lessen frequency

Question 44

what is exchange transfusions used to treat?

Answer 44

severe hyperbilirubinaemia and anaemia secondary to HDFN

Question 45

what is the aim of exchange transfusions?

Answer 45

to remove antibody coated red cells and excess bilirubin and increase haemoglobin

Question 46

what causes such a high risk from IUT's?

Answer 46

cardiac complications, biochemical and haematological disturbances

Question 47

what is the indications for a IUT?

Answer 47

severe hyperbilirubinaemia caused by HDFN, symptoms of ABH

Question 48

what conditions worsen HDFN?

Answer 48

septicaemia, metabolic disease and DIC

Question 49

what are the requirements of top up blood?

Answer 49

O-, CDE-, Kell-, CMV-, first time donors, same donor and preferably male