Lecture 6 - Neonatal Testing Flashcards
what is HDFN?
haemolytic disease of the foetus and newborn
how does HDFN occur?
when the mother has IgG antibodies in her blood that cross the plasma and bind to foetal red cells that possess the corresponding antigen
what is hydrops fetalis?
heart failure in utero
how can HDFN cause heart failure in utero?
the anaemia causes cardiac decompensation due to lack of red cells
what is extramedullary erythropoiesis?
red cells being produced in an unusual location
how can HDFN cause jaundice?
the removal of the erythrocyte antibody complex from foetal blood circulation causes haemaglobin degradation so causes increased unconjugated bilirubin levels
how does bilirubin levels cause neurological damage? what is this called?
called kernicterus and it is caused by bilirubin accumulating in the grey matter of neurological tissue causing neurotoxic effects
how is the neurotoxicity caused in kernicterus?
mass destruction of neurones via apoptosis and necrosis
what are the symptoms of acute bilirubin encephalopathy?
legarthy, decreased feeding, hypotonia/hypertonia, high-pitched cry, fever, seizures or death
what are the features of chronic bilirubin encephalopathy?
movement disorders, auditory dysfunction, oculomotor impairments, impaired digestive function, gastroesophageal reflex
what is different in relation to HDFN with an IgG antibody and an anti-Kell antibody?
anti-kell can cause severe anaemia regardless of the strength of the antibody
what are the effects of an anti-Kell antibody on red blood cells?
it suppresses the bone marrow so inhibits erythroid pregenitor cells, prevents formation of blood cells
what are the microbiology antenatal tests?
HPB, HIV, syphilis
what are the transfusion antenatal tests?
ABO group, antibody screening, ffDNA
when do microbiology and transfusion tests occur?
8-12 weeks gestation
what is the purpose of 28 week tests?
to confirm ABO and RhD group, for detection and identification of alloantibodies
how is the genotype of the baby determined?
using PCR on free foetal DNA in the mothers circulation
what is the ffDNA genotyping sensitive for?
RhD, C, c, E, e and Kell
what concentration of anti-D levels cause referral to a foetal medicine specialist?
above 4IU/mL
what concentration of anti-c causes referral to foetal medicine specialist?
above 7.5IU/mL
what type of antibodies are quantified?
anti-D and anti-c
how does quantification work?
amount of agglutination the antibody causes compared to the standard that runs at the same time
what machine does quantification occur in?
continuous flow analyser
what antibodies are used in titration?
anti-K, anti-E, anti-Fya
how does the titration reaction occur?
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
how does anti-D Ig injection work?
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
what is RAADP?
routine antenatal anti-D prophylaxis
how much RAADP is administered and when?
15000 IU at 28 weeks gestation
what patients are given RAADP?
those who are RhD negative that have RhD positive baby
what causes foeto-maternal haemorrhage?
foetal blood crosses maternal circulation
how much FMH can the dosage of RAADP given protect against?
12mL for 1500IU
when should as assessment of FMH occur?
following a sensitising event on a RhD negative woman, following delivery of RhD positive baby, following stillbirth/IUD on negative or positive women
what is the acid equation method?
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
how does flow cytometry occur?
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
why cant flow cytometry be used on a RhD positive woman?
because an anti-D fluorochrome antibody is used
when is suspected HDFN investigated?
when unexpected jaundice occurs, babies born to mothers with known alloantibodies
how is HDFN investigated?
test for maternal antibodies, test for ABO incompatibility
how is HDFN investigation performed?
ABO and RhD grouping performed on mother and baby samples, antibody screening panel and NAT on baby sample
what blood group does a mother usually belong to when HDFN occurs?
usually a group O with a group A/B baby
what is the doppler ultrasound?
determines the middle cerebral artery peak systolic velocity, which indicates the severity of the foetal anaemia
what things indicate the need for foetal blood sampling?
severe anaemia before 24 weeks gestation, if there has been a post IUD, if there is an increase in maternal red cell alloantibody levels
what is the purpose of IU transfusions?
prevent life threatening foetal anaemia and allow pregnancy to continue until the baby is viable
how are IU transfusions adapted to lower the risk?
started as late as possible, and maximum safe volume with maximum haemocrit is given to lessen frequency
what is exchange transfusions used to treat?
severe hyperbilirubinaemia and anaemia secondary to HDFN
what is the aim of exchange transfusions?
to remove antibody coated red cells and excess bilirubin and increase haemoglobin
what causes such a high risk from IUT’s?
cardiac complications, biochemical and haematological disturbances
what is the indications for a IUT?
severe hyperbilirubinaemia caused by HDFN, symptoms of ABH
what conditions worsen HDFN?
septicaemia, metabolic disease and DIC
what are the requirements of top up blood?
O-, CDE-, Kell-, CMV-, first time donors, same donor and preferably male
