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Flashcards in The Blood Transfusion Laboratory Deck (36)
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1

What is present on the surface of red blood cells? 

Antigens 

2

Where are antibodies found and what are they? 

  • Antibodies are found in the blood plasma 
  • They are immunoglobulins produced by the immune system following exposure to a foreign antigen 

3

What immunoglobulin antibodies are there present in the blood? 

IgG (RhD) and IgM (Anti-A and Anti-B) 

4

When does a blood reaction occur? 

 

When an antibody in the plasma reacts with an antigen on cells 

5

What is the effect of antigens in transfused blood? 

  • Foreign antigens in transfused blood will stimulate a patient to produce the antibodies only if the patient lacks the antigen (non-self) 
    • The frequency of antibody production is very low, this frequency will increase as more transfusions are given 

6

What will stimulate antibody production? (3)

  • Blood tranfusion 
    • Blood carrying antigens foreign to patient 
  • Pregnancy 
    • Foetal antigen entering maternal circulation during pregnancy 
  • Environmental factors 
    • Naturally acquired e.g Anti-A and Anti-B

7

What are the two types of antibody-antigen reactions?  

  • in vivo (in the body) 
    • leads to destruction of the cell (e.g transfusion causing haemolysis) either 
      • directly = cell breaks up in bloodstrem (intravascular) 
      • Indirectly = liver and spleen remove antibody coated cells (extravascular) 
  • In vitro (laboratory) 
    • Seen in agglutination tests 

8

What is agglutination? 

The clumping together of red cells into visible agglutinates by antigen-antibody reactions to to the cross-linking of antibodies with antigens 

9

What can agglutination identify? 

  • The presence of a red cell antigen 
    • I.e blood grouping 
  • The presence of an antibody in the plasma 
    • Antibody screening/ identification 

10

What is the clinical significance of the ABO grouping system? 

  • If you transfuse red cells without knowing the patients blood group the chance of an interaction will be quite high
  • ABO antibodies can active complement and cause INTRAVASCULAR HAEMOLYSIS 

11

What is the inheritance of blood groups? 

  • A and B genes are dominant 
  • O is recessive 
    • 2 chromosomes are inherited (one from each parent) x 3 alleles = 6 possible combinations 
      • AA, AB, BB, BO, OO, AO 

12

What does co-dominance mean? 

Co-dominance means when both alleles are equally expressed and hence both contribute to the phenotype of the heterozygote. 

This happens when AB genotype as they are both dominant 

13

If you have the OO genotype what red cell antigens and antibodies will you have? 

  • Phenotype will be blood group O 
  • You will have no red cell antigens 
  • You will have anti-A and anti-B antibodies 

14

If you have the AB genotype what red cell antigens and antibodies will you have? 

  • You will have the AB phenotype 
  • You will have A and B antigens 
  • You will have no red cell antibodies 

15

How do we find out the blood group of a particular patient? 

Patients red cells and plasma are both tested 

  • This allows us to work out what antigens are on the surface of the red blood cells and what antibodies are present in the plasma 

16

How do we test a patients red cells to find out the presence of antigens? 

  • The gel matrix will be impregnated with anti-A, anti-B and anti-D antibodies 
    • Agglutination will show that there is a particular antigen on the red cells 
    • No agglutination shows the antigen is absent 
      • Red cells will pass through the gel matrix, unless there is agglutination = big agglutinate will not pass through and stay at the top 

17

What would the blood type be of this person where we have added red blood cells to tubes with anti-A, anti-B and anti-D  (forward) and plasma to the tubes with red blood cells (reverse)? 

Blood group A as there is agglutination when the red cells were added to the anti-A test tube 

 

If it were AB = agglutination in both, if it were O = no agglutination in the wells, no antigens present

18

How do we test a patients plasma to find out the presence of antibodies? 

  • Gel matrix impregnated with A cells and B cells 
    • Agglutination shows that a particular antibody is in the plasma or serum 
    • No agglutination shows that the antibody is absent 

19

Explain why blood group O is considered the universal donor

  • If you are blood group O you will have neither A nor B antigen 
  • Therefore, whatever antigens are in the recipients plasma there will be no interaction and agglutination 
  • Blood group O can donate blood to all blood groups 

20

Explain the Rh grouping system 

  • Second most important after ABO 
  • People with the D antigen are RhD positive (85% of UK) 
  • People who do not produce any D antigen are RhD negative 
    • 4 main others are C,c,E and e 

21

What is the clinical significance of the Rh antigen in transfusion reactions? 

  • D antigen is very immunogenic and anti-D is easily stimulated = PREVENTION 
  • All Rh antibodies are capable of causing a severe transfusion reaction - ANTIBODY DETECTION 

22

What is the clinical significance of the Rh antibodies in pregnancy? 

  • Rh antibodies are usually IgG and can cause haemolytic disease of new-borns 

23

Explain haemolytic disease of newborn (HBN)? 

  1. Rh+ father so foetus in Rh- mother is Rh+ 
  2. Rh antigens from foetus can enter mothers blood during delivery 
  3. In response to foetal Rh antigens, mother will produce anti-Rh antibodies 
  4. If a women becomes pregnant with another Rh+ foetus her anti-Rh antibodies will cross the placenta and damage foetal RBCs 

24

How can we avoid haemolytic disease of newborn? 

  • Carry out blood group and antibody screening at antenatal booking to identidy pregnancies at risk of HDN 
    • RhD negative women may need anti-D prophylaxis 
  • Blood group and antibody screen at 28 weeks 
  • Atypical antibodies are quantified periodically to asses their effect in the foetus 

25

What treatment can we give a mother if she has identified as Rh-D and is carrying RhD+ foetus? 

Routine Antenatal Anti-D prophylaxis 

Injection of anti-D to bind and remove any foetal RhD+ in the maternal circulation 

26

When is the anti-D injection administered? 

  • 1500 iu of anti-D is given routinely at 28 weeks and a smaller dose (usually 500 iu) after delivery if baby RhD+
  • In some hospitals 2 smaller (500 iu) doses are given at 28 and 34 weeks instead of the 1 larger dose
  • Anti-D is also given after any event which may cause a feto-maternal haemorrhage (bleed between mum and fetus) such as:
    • Abdominal trauma
    • Intrauterine death
    • Spontaneous or therapeutic abortion

27

How is antibody screening carried out for other clinically significant antibodies that can cause a haemolytic reaction? 

  • To detect for these antibodies 
    • Patients serum is mixed with 3 selected screening cells containing relevant antigens, incubated for 15 minutes at 37 degrees + centrifuged 
    • Clinically significant ABs reacting at body temp are detected and identified using a panel of phenotyped red cells 

28

Why is it important to screen and identify antibodies that cause haemolytic reactions? 

It is important that we screen for these antibodies so that if detected, antigen negative blood can be provided to avoid stimulating an immune reaction 

29

What is the zeta potential? 

Posotively charged ionic cloud that surrounds red blood cells 

30

What is the issue of this zeta potential (posotively charged ionic cloud surronding RBCs)? 

  • Red cells are not able to come in close proximity with the zeta potential 
    • E.g pentameric IgM (anti-A and anti-B) antibody diameter allows agglutination but IgG antibody diameter too small to allow agglutination 
      • For the IgG antibodies we need to get rid of the ionic cloud 

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