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3RD YEAR SYSTEMS: Haematology/Immunology > Blood Transfusion > Flashcards

Blood Transfusion Flashcards

1
Q

What differentiates blood groups?

A

Blood groups are defined by the presence of specific antigens (carbohydrate sugars) on the surface of red blood cells

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2
Q

What happens if you are transfused with blood from a different blood group?

A
  • You can provoke an antibody response
  • The response varies in severity depending on the antigens involved in the interaction
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3
Q

What are the 4 common blood groups in the ABO system?

A

ABO are expressed on the surface of RBCs. You can have the following blood types:

  • Type A – A antigens
  • Type B – B antigens
  • Type AB – a mixture of A and B antigens
  • Type O – don’t have A and don’t have B but don’t have anything to make up for these
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4
Q

Structurally, what are antigens that are found on the surface of red blood cells?

A

They are sugars

  • The ABO gene encodes glycosyltransferase which adds glycans to proteins or lipids on RBCs
    • A and B genes code for transferase enzymes
    • But the ‘O’ gene is a non-functional allele
  • So therefore A and B are (co-)dominant (if you get both you are AB) and O is recessive
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5
Q

What is the name given to the antigen on RBCs in Type A blood group?

A

N-acetyl-galactosamine

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6
Q

What is the name given to the antigen on RBCs in Type B blood group?

A

Galactose

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7
Q

Individuals naturally develop antibodies against the ABO antigens they do not have. So therefore:

  1. Group A will develop antibodies against _____?
  2. Group B will develop antibodies against _____?
  3. Group O will develop antibodies against _____?
  4. Group AB will develop antibodies against ____?
A
  1. Group A will develop antibodies against B (anti-B antibodies)
  2. Group B will develop antibodies against A
  3. Group O will develop antibodies against A and B
  4. Group AB have no antibodies
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8
Q

Immune tolerance

A
  • You induce active immune tolerance from birth (differentiate between self vs non-self)
  • If you are blood group A, you will not develop antibodies against A unless you develop some form of autoimmune haemolytic anaemia later in life
  • Anti-A and anti-B antibodies are found in the sera of individuals who lack the corresponding antigens. They are produced in response to environmental stimulants, such as bacteria, and have therefore been termed natural antibodies. The antibodies formed to carbohydrate antigens are mostly immunoglobulin M (IgM). IgM antibodies activate complement, which, in conjunction with the high density of ABO antigen sites on RBCs, is responsible for the severe, life-threatening transfusion reactions that may be caused by ABO-incompatible transfusions.
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9
Q

IgM antibody/immunoglobulin and its characteristics

A
  • IgM is produced first upon antigen invasion and increases transiently
  • We have naturally occuring anti-A/B antibodies due to
  • It can fix complement
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10
Q

Which blood group can donate/receive to who?

A
  • If you are Type A you can donate to people with blood group A and AB
  • If you are Type B you can donate to people with blood group B and AB
  • If you are group AB you can only donate to people with type AB
  • If you are group O you can donate to all blood group types
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11
Q

Which pairs of blood groups cannot donate/receive blood due to chance of severe reaction?

A

A cannot donate to B and O

B cannot donate to A and O

AB cannot donate to A, B or O

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12
Q

What are the rules with Fresh Frozen Plasma donation?

A

Broadly speaking the reverse of Red Cell donation is true for plasma donation as plasma contains antibodies

  • If you have a patient who is Type A then they will have A antigens on the surface of their RBCs. If you have a Group B donor they will have anti-A antibodies in their plasma so you can get a reaction and therefore this cannot be done.
  • However, the reactions for plasma are usually much less severe than RBCs
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13
Q

What is the RhD blood group system?

A

Each of the 4 ABO blood groups can be either RhD positive or RhD negative, which means in total there are 8 blood groups.

Genotypes = DD, Dd or dd

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14
Q

How do RhD negative individuals make anti-D antibodies?

A

If they are exposed to RhD+ cells either through transfusion or pregnancy (if the foetus expresses a paternally encoded RhD +ve cell).

  • Anti-RhD antibodies can cause transfusion reactions (second in severity to ABO reactions) or result in haemolytic disease where the anti-RhD/anti-D antibodies that the mother makes destroy the foetus’ RBCs
  • So pregnant women are screened for anti-D antibodies to avoid this
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15
Q

Why might we give a patient a blood transfusion?

A
  • To correct severe acute anaemia, which might otherwise cause organ damage
  • To improve QOL in patient with otherwise un-correctable anaemia
  • To prepare a patient for surgery or speed up recovery
  • To reverse damage caused by patient’s own red cells i.e in Sickle Cell Disease
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16
Q

1 unit of blood (roughly 1 bag) will increment the Hb by how much?

A

by 5g/L

17
Q

When is a platelet transfusion indicated?

A
  • Massive haemorrhage
  • Bone marrow failure
  • Prophylaxis for surgery
  • Cardiopulmonary bypass - use only if bleeding
18
Q
  1. 1 dose of platelets is equal to how many blood donations?
  2. By how much does it increment the platelet levels?
A
  1. 1 dose = 4 pooled donations or 1 apheresis donor (donates a lot of blood over a few hours)
  2. 20-40.10^9/L
19
Q

Fresh frozen plasma

  1. What is it?
  2. Indications?
  3. Lab tests?
A
  1. The plasma you get from 1 unit of blood stored frozen. If ever you need it you have to let it thaw for 30-60 mins
  2. Massive haemorrhage (approx 1 unit FFP: 1 bag of RBCs), Disseminated intravascular coagulation (DIC) if they are bleeding or prophylactic (expected to bleed such as in liver failure where they are missing coagulation factors)
20
Q

As a junior doctor, if you ask the Blood Bank for a blood sample they will do something called ‘group and screen/save’. What does this mean?

A
  • Check ABO and RhD type - gel columns and automation or coombs test
  • Checked against historical records
  • Screen for allo-antibodies in serum
21
Q

What is the Coombs Test / direct or indirect anti-globulin test (DAT/IAT)?

A

A test that looks for IgG antibodies on the surface of RBCs that may attack and destroy the cell. This is because IgG antibodies are bivalent and link together/bridge across RBCs and cause agglutination/clumping which is picked up in the test.

There are 2 types:

  • Direct coombs / direct anti-globulin test
  • Indirect coombs / indirect anti-globulin test
22
Q

What is the direct coombs / anti-globulin test and what is it used to diagnose?

A

A direct test takes a blood sample and looks for antibodies on the surface of the RBCs

  • Detects autoimmune haemolytic anaemia - patient is producing antibodies that are attacking their own RBCs
  • Detects Haemolytic Transfusion reactions
23
Q

What is the indirect coombs / anti-globulin test?

A

Indirect test adds an external antibody to see if it binds to the surface of RBCs. If it does cross-link then agglutination occurs which could be fatal.

Use this in cross matching - testing for harmful interactions between patient and donor’s blood

24
Q

Are ABO and Rh blood systems reactive at 37%?

A

Usually yes

25
Q

Describe the development of maternal Anti-D antibodies

A
  • So 15% of mothers are RhD negative
  • The only way they produce anti-D antibodies is through exposure and this can be via transfusion or pregnancy
  • Most men are RhD +ve and so they expose the mother via the baby
  • If RBCs leak across the placenta into the mother’s circulation either during pregnancy or particularly at birth then the mother will pick up these foreign RhD antigens and form anti-D antibodies (tend to be protein so - IgG)
  • The IgG crosses over the placenta from the mother and can cause severe alloimmune haemolysis in the baby.
  • The baby then becomes profoundly anaemic and can develop cardiac failure and die
26
Q

What is Alloimmunity?

A

Alloimmunity (sometimes called isoimmunity) is an immune response to non-self (foreign) antigens from members of the same species

27
Q

What are alloantibodies?

A

Alloantibodies are immune antibodies that are only produced following exposure to foreign RBC antigens (such as in transfusion causing haemolytic transfusion reactions or pregnancy)

28
Q

Anti-D screening is routine at what stage of pregnancy? What is this preventing?

A

28 weeks

Done to prevent Hemolytic disease of the newborn

3RD YEAR SYSTEMS: Haematology/Immunology (15 decks)

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