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Transfusion Science > ABO system > Flashcards

ABO system Flashcards

1
Q

What is the most common blood group in Ireland

A

O+

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2
Q

What is the least common blood group in ireland

A

AB-

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3
Q

Who was the ABO blood group system first described by and when?

A

Karl Landsteiner in 1901

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4
Q

Why is the ABO system the most clinically important blood group system in transfusion

A
  • Nature of the ABO antibodies -> they are mainly IgM and cause intravascular haemolysis of incompatible red cells via complement activation.
  • ABO incompatibility accounts for a significant number of fatal haemolytic transfusion reactions.
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5
Q

Reasons for severe haemolytic transfusion rxns (4)

A
  1. Mislabelling of blood sample -> patient sample A being labelled with patient B details for blood grouping
  2. Mislabelling donated blood packs -> blood packs are labelled with the name and other identifiers of patient receiving the blood
  3. Transfusing the wrong patient
  4. Serological errors -> patient or donor blood misgrouped in the lab
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6
Q

Where are the three common alleles (A, B and O) located

A

At the ABO locus on chromosome 9

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7
Q

What is located on chromosome 19

A

The H and h alleles

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8
Q

What are the foundation blocks for the building of the ABO blood group antigens

A

Oligosaccharide chains

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9
Q

Where are these oligosaccharide chains found

A

Red blood cells have the oligosaccharide chains attached to the membrane

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10
Q

What does the H gene code for

A

The transferase enzyme that adds fucose to the precursor oligosaccharide chains on the red cell membranes

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11
Q

What does the H antigen act as

A

The precursor material on which A and B antigens are built

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12
Q

What do the A and B genes encode

A

A transferase enzyme

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13
Q

What does the transferase enzyme encoded by the A and B genes do

A

It acts upon the H precursor antigen material to produce the A and B antigen

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14
Q

What is the O gene known as and why

A

It is known as an amorph (is silent). This is beacuse the O gene does not encode a functional enzyme and therefore does not produce a detectable antigen

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15
Q

What do the red cells of a group O person have

A

An abundant amount of H antigen but no A or B antigens

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16
Q

What is the full name of the enzyme that the A gene codes for

A

Alpha 1,3-Nacetyl-galactosaminyltransferase

17
Q

How is the A antigen produced

A

The enzyme alpha 1,3-Nacetylgalactosaimyltransferase uses the H antigen as a substrate and catalyses the addition of the sugar N-acetyl galactosamine to the terminal galactose of the oligosaccharide chain to produce the A antigen
The A enzyme can only produce the A antigen if a H antigen is already present

18
Q

What is the full name of the enzyme that the B gene codes for

A

Alpha 1,3-galactosyltransferase

19
Q

How is the B antigen produced

A

The enzyme 1,3-galactosyltransferase uses the H antigen as a substrate and catalyses the addition of the sugar D-galactose to the terminal galactose of the oligosaccharide chain to produce the B antigen

20
Q

What is the Bombay blood group

A
  • A rare case where individuals are homozygous for the h allele (lack the H gene) and cannot form the H antigen,the precursor for the A and B antigens
  • Bombay red cells type as blood group O
  • The serum of a Bombay individual contains Anti H, Anti A and Anti B and will react if transfused with blood that contains the A, B or H antigens
  • Bombay blood frozen for emergency requirements
21
Q

What are ABO antibodies thought to be stimulated by?

A

Bacteria, viruses and other environmental antigens. (Bacteria and viruses known to contain structures that are chemcally similar to human A and B antigens and can stimulate the production of Anti A and Anti B in individuals who lack these)

22
Q

What type of antibody are most ABO antibodies

A

IgM antibodies, however some individuals also have some IgG (at low levels)

23
Q

How long after birth can ABO antibodies be demonstrated

A

3-6 months after birth

24
Q

What temp do ABO antibodies best react at? (mainly IgM antibodies)

A

4-22 degrees C

25
Q

The absence of ABO antibodies can be seen in who? (4)

A
  1. New borns
  2. Infants (under 4-6 months)
  3. Hypogammaglobinaemia patients -> unable to produce antibodies
  4. Patients on chemo or radium tx
26
Q

A decrease in the level of ABO antibodies may be seen in who? (1)

A

Elderly patients

Transfusion Science (6 decks)

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