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Haem (not Zara) > Blood transfusion > Flashcards

Blood transfusion Flashcards

1
Q

What is the blood group?

A

The combination of RBC antigens presesnt

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2
Q

What is a blood group system?

A

A collection of one or more RBC antigens under the control of a single gene or a cluster of closely linked homologous genes

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3
Q

What are the most clinically significant blood systems?

A

The ABO and Rh blood group systems

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4
Q

How is the clinical importance of a blood group system determined?

A

Depends on the capacity of antibodies against the specific RBC antigens to cause haemolysis of RBCs

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5
Q

What is haemolytic transfusion reactions (HTRs)

A

The tranfused RBCs have the antigen which corresponds to the antibody in the patient’s plasma causing haemolysis

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6
Q

What is haemolytic disease of the fetus and the newborn

A

The fetus has an RBC antigen inherited from the father and the mother has produced an antibody to the fetal RBC antigen that has crossed the placenta.

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7
Q

How are ABO antibodies produced

A

Production is stimulated when the immune system encounters the ‘missing’ ABO blood group in foods or in microorganisms

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8
Q

What class are ABO antibodies?

A

IgM antibodies that do not class switch

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9
Q

How do IgM ABO antibodies cause acute HTRs? What does this result in?

A
  • Activation of the complement system
  • Massive intravascular haemolysis
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10
Q

Do ABO antibodies cause HDFN? Why, why not?

A

NO because they cannot cross the placenta.

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11
Q

How are acquired antibodies formed?

A

Acquired antibodies are formed as a result of active immunisation (alloimmunisation) to ‘non-self’ RBC antigens following exposure to RBCs from another individual. eg during non matched blood transfusion

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12
Q

What class are acquired antibodies?

A

IgG antibodies

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13
Q

Although most ABO antibodies are IgM, there can also be a small amount of naturally occurring IgG ABO antibodies in plasma. These IgG ABO antibodies can cross the placenta but don’t usually cause HDFN. Give 2 reasons why.

A
  • Foetal red cells have poorly developed ABO antigens
  • ABO antigens are found on numerous other cells
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14
Q

What type of HTRs to IgG antibodies cause?

A

delayed HTRs
- Cause mainly extravascular haemolysis but not massive intravascular haemolysis

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15
Q

Can IgG antibodies cause HDFN? Why, Why not?

A

Yes because they can cross the placenta

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16
Q

Which antigens does each blood group express on their RBCs?

A

There are 4 main blood groups within the ABO blood group system: A, B, AB and O.
- Group A individuals express A antigen on their RBCs
- Group B individuals express B antigen on their RBCs
- Group AB individuals express both A and B antigens on their RBCs
- Group O individuals express neither A nor B antigens on their RBCs

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17
Q

How are A and B antigens formed?

A
  • By adding specific monosaccharides onto a common glycoprotein and fucose stem (the ‘H antigen’) on the RBC membrane.
  • The monosaccharide added is determined by the corresponding gene
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18
Q

Describe the inheritance patterns of the ABO blood group system

A

A and B are codominant and O is recessive.

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19
Q

What does Landsteiner’s law state?

A

States that whichever ABO antigens are lacking on a given person’s RBCs, that person will always have the antibodies for these ABO antigens

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20
Q

Why is group O the universal donor?

A

Group 0 red cells lack both A and B antigens therefore there is no risk of acute HTR occuring.

21
Q

Why do platelets of the same ABO group as the patient have to be selected for transfusion?

A
  • Reduces risk of a poor response due to anti A or B antibodies in the patient’s plasma causing destruction of the transfused platelets.
  • Reduce risk of haemolysis of the patient’s red cells by anti-A or anti-B antibodies in the transfused unit of platelets (platelets are suspended in plasma)
22
Q

When can platelets/FFP/cryoprecipitate of other ABO groups be given?

A

If the patient is classed as high titre negative (low levels of anti A or B antibodies in plasma)

23
Q

What is the most important antigen in the Rh system

A

D

24
Q

Describe the inheritance of the D antigens in the Rh system

A

Inheritance is controlled by one gene. D allele is dominant and codes for D antigen, d allele codes for no D antigen

25
Q

Anti-D antibodies are clinically significant as they can cause what 2 things?

A
  • Delayed HTRs (extravascular haemolysis resulting in anaemia, high bilirubin, jaundice)
  • HDFN (negative mother carries positive fetus and IgG anti-D antibodies from mother can cross the placenta and haemolyse the fetal RBCs)
26
Q

How is HDFN treated when the mother is RhD negative and the fetus is RhD positive?

A

Formation of anti-D antibodies is prevented by giving the mother anti-D immunoglobulin which destroys RhD positive fetal RBCs in the mother’s circulation.

27
Q

How is a patient’s ABO group determined?

A

1) Forward group tested
- ABO antigens on RBCs identified by adding anti ABO antibodies to a sample of patient’s RBCs.
2) Reverse group tested
- Presence or absence of ABO antibodies in plasma tested by mixing serum with A and B RBCs
* AGGLUTINATION IS THE SIGN

28
Q

How is patients RhD type determined?

A

By testing a sample of the patient’s RBCs against reagent anti-D antibodies.
Interaction between the regent anti-D antibodies will results in agglutination that can be seen.

29
Q

How are acquired alloantibodies tested for?

A
  • The patient’s serum is tested against panels of RBCs which together are known to express all of the clinically relevant RBC antigens.
  • Agglutination is visualised by adding anti-human globulin.
30
Q

How is a cross match performed?

A

The patient’s plasma against a sample of RBCs from the unit of red cells selected for transfusion.
Agglutination shows the cells are incompatible.

31
Q

What are the two types of testing that blood donations undergo?

A
  • Group and screen
  • Infection screening
32
Q

What is group and screen?

A
  • ABO and RhD blood group determined
  • Other clinically significant antibodies are tested for
33
Q

What is infection screening?

A

Blood is tested for infections to reduce risk of transfusion transmitted infections.
Donors are also screened to identify other infections with no blood test

34
Q

What are the 2 methods by which blood is collected?

A

1) Whole blood donation
2) Apheresis

35
Q

What is whole blood donation?

A

Blood is collected from a donor in its entirety and then separated (via centrifugation) into its component parts later in the laboratory.

36
Q

What are the advantages of apheresis?

A
  • allows specific blood components to be collected
  • allows donors to maximize their donations as a larger volume can be collected of the specific component
37
Q

What is apheresis?

A

1) The donor is connected to an apheresis machine.
2) Blood from the donor passes through the machine which separates out the particular component required.
3) The remainder of the blood is returned to the donor.

38
Q

What are the major blood components?

A

1) Red cells
2) Platelets
3) Fresh frozen plasma (FFP)
4) Cryoprecipitate

39
Q

What is fractionation?

A

When plasma donations are pooled together for the manufacture of the following plasma derived products:
1) Human albumin solution
2) Immunoglobulins
3) Clotting factor concentrates

40
Q

What are red cell transfusions used for?

A
  • To increase Hb and thus O2 carrying capacity of blood in patients w/ anaemia or blood loss
41
Q

What are platelet transfusions used for?

A
  • To treat bleeding
  • To reduce the risk of bleeding in patients with low platelet counts (eg. thrombocytopenia or platelet dysfunction due to certain drugs)
42
Q

What does FFP contain and what is it used for?

A

Contains: All the coagulation factors
Used for: treatment of bleeding or reduce the risk of bleeding in patients with coagulopathies (multiple clotting factor deficiencies)

43
Q

What are the causes of coagulopathies?

A

Dilution and comsumption

44
Q

Why is FFP frozen?

A

Low temperature maintains the activity of the clotting factors

45
Q

Why does cryoprecipitate contain and what is it used for?

A

Contains: Fibrinogen, factor 8, VWF and factor 13
Used For: Treating bleeding or to reduce risk of bleeding especially when fibrinogen is low (eg. as a result of haemorrhage or DIC)

46
Q

How is cyroprecipitate made?

A

Slow thawing of FFP until there is a precipitate.
The ppt is then re-suspended in a small volume of plasma and frozen

47
Q

When is Human albumin solution used

A
  1. To replace plasma volume in patients with plasma volume loss e.g. due to burns or trauma
  2. To replace plasma in plasma exchange e.g in the treatment of autoimmune disorders
  3. To initiate diuresis in patient with low albumin e.g. due to liver or kidney disease
48
Q

What are the two types of immunoglobulin?

A
  1. NORMAL IMMUNOGLOBULIN
    - This contains antibodies to viruses that are common in the population.
    - Intramuscular normal immunoglobulin may be used to protect susceptible contacts against infection e.g. hepatitis A, measles or rubella.
    High-dose intravenous immunoglobulin is used as replacement therapy in patients with severe immunoglobulin deficiency and in the treatment of autoimmune diseases e.g. idiopathic thrombocytopenic purpura (ITP).
  2. SPECIFIC IMMUNOGLOBULIN
    - This is made from selected donors with high antibody levels to the target of treatment (‘hyperimmune donors’).
49
Q

A man and a woman enter an emergency department with huge blood loss. They are given emergency transfusions; the man is given O positive and the woman is given O negative. Why?

A
  • The anti D antibodies formed are IgG which do not have a huge effect on RBCs as ABO antibodies are present on other cells so IgG can bind to themselves.
  • However, the woman could be pregnant or planning to get pregnant therefore if the foetus is RhD positive and she is negative, by being given a positive transfusion she could form IgG anti-D antibodies which can pass through the placenta and haemolyse fetal red cells.

Haem (not Zara) (4 decks)

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