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CLINICAL PATHOLOGY > The Blood Transfusion Laboratory > Flashcards

The Blood Transfusion Laboratory Flashcards

1
Q

What is present on the surface of red blood cells?

A

Antigens

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2
Q

Where are antibodies found and what are they?

A
  • Antibodies are found in the blood plasma
  • They are immunoglobulins produced by the immune system following exposure to a foreign antigen
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3
Q

What immunoglobulin antibodies are there present in the blood?

A

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

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4
Q

When does a blood reaction occur?

A

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

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5
Q

What is the effect of antigens in transfused blood?

A
  • 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
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6
Q

What will stimulate antibody production? (3)

A
  • 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
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7
Q

What are the two types of antibody-antigen reactions?

A
  • 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
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8
Q

What is agglutination?

A

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

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9
Q

What can agglutination identify?

A
  • The presence of a red cell antigen
    • I.e blood grouping
  • The presence of an antibody in the plasma
    • Antibody screening/ identification
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10
Q

What is the clinical significance of the ABO grouping system?

A
  • 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
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11
Q

What is the inheritance of blood groups?

A
  • 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
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12
Q

What does co-dominance mean?

A

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

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13
Q

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

A
  • Phenotype will be blood group O
  • You will have no red cell antigens
  • You will have anti-A and anti-B antibodies
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14
Q

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

A
  • You will have the AB phenotype
  • You will have A and B antigens
  • You will have no red cell antibodies
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15
Q

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

A

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
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16
Q

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

A
  • 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
Q

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)?

A

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
Q

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

A
  • 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
Q

Explain why blood group O is considered the universal donor

A
  • 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
Q

Explain the Rh grouping system

A
  • 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
Q

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

A
  • 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
Q

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

A
  • Rh antibodies are usually IgG and can cause haemolytic disease of new-borns
23
Q

Explain haemolytic disease of newborn (HBN)?

A
  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
Q

How can we avoid haemolytic disease of newborn?

A
  • 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
Q

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

A

Routine Antenatal Anti-D prophylaxis

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

26
Q

When is the anti-D injection administered?

A
  • 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
Q

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

A
  • 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
Q

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

A

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
Q

What is the zeta potential?

A

Posotively charged ionic cloud that surrounds red blood cells

30
Q

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

A
  • 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
31
Q

How we get IgG antibodies to interact with cells and remove the zeta potential?

A

LISS (Low ionic strength saline)

  • This will counteract the zeta potential
32
Q

What is the indirect anti-globulin test (IAT) used for?

A
  • Use for
    • Screening for antibodies (IgG)
    • Identifying antibodies
    • Cross-matching donor blood with recipient plasma when there are known antibodies or a previous history of antibodies
33
Q

What is cross-matching?

A

Testing for agglutination of the donors RBC’s by the recipients serum and vice versa

34
Q

What are the types of cross-matching we can do?

A
  • Immediate spin crossmatch (ISX)
    • Must have had a negative antibody screen
    • Checking donor red cells against patient’s plasma
    • ABO check
    • Incubate for 2-5 minutes room temperature, spin and read
  • Full Indirect Antiglobulin test (IAT) crossmatch
    • Antibody screen positive or patient has known antibody history
    • Select antigen negative donor red cells and incubate with patient serum for 15 minutes at 37 degrees
35
Q

How do we test donor blood?

A
  • Blood Establishment:
    • MHRA licensed manufacturer of blood and products
  • Donor Selection
    • Questionnaire: lifestyle, health, not previously transfused
      • Collection procedure arm cleansing / diversion pouch
  • Comprehensive testing of all products
    • Viral
      • HIV 1+2
      • Hepatitis B
      • Hepatitis C
      • Syphilis
      • HTLV
    • Platelets
      • Bacteria
  • ABO, RhD, K, antibody screen
36
Q

What are the blood components for donation?

A
  • Red Cells
  • Fresh Frozen Plasma (given for coagulopathy + associated bleeding)
  • Platelets (used to create clots to reduce bleeding)
  • Cyroprecipitate (contains factor VII, vWF and fibrinogen, used for peoples whos blood doesnt clot properly for example Haemophilia or vWdisease)

CLINICAL PATHOLOGY (52 decks)

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