ABO System Flashcards
How many blood groups are there?
8
what are the two systems used to classify blood
ABO system and Rhesus system
What are the 4 groups in the ABO system
O, A, B and AB
What is the most common blood type in Ireland?
O+
What is the least common blood group in Ireland?
AB-
Who came up with the ABO system>
Karl Landsteiner in 1901
Write a sentence to describe the relationship between antigens on red cells and plasma/serum antibodies
The plasma contains the opposite antibody to the antigen found on the red cell. i.e A antigen on red cell = B antibody in plasma/serum
What type of antibody are ABO antibodies?
IgM
When might a Haemolytic Transfusion Reaction occur?
when a patient has been transfused with the wrong blood type, usually due to mislabeling of a blood sample, mis-grouping of blood donations or transfusing the wrong patient
What chromosome are the A, B and O alleles found on?
chromosome 9 at the ABO locus
Which chromosome are the H and h alleles found on?
chromosome 19
what are olgiosaccharide chains?
are attached to the membrane of the RBCs, and are the foundation blocks for the building of the ABO blood group antigens
What does the H gene do?
codes for a transferase enzyme which adds fucose to olgiosaccharide chains on the red cell membrane.
What is the function of the H antigen
is the precursor material on which A and B antigens are built
How are the A and B antigens formed?
A and B genes code for a transferase enzyme. This acts on the H precursor antigen which produces the A and B antigen
the O gene is an amorph, what does this mean?
it does not encode a functional enzyme, meaning no detectable antigen is produced.
does group O contain more or less of H antigen than A, B or AB groups?
they have more H antigen
what enzyme does the A gene code for?
alpha 1,3-Nacetyl-galactosaminyltransferase
how does alpha 1,3- Nacetyl-galactosaminyltransferase work?
it uses H antigen as a substrate, and catalyses the addition of the sugar N- acetyl galactosamine to the last galactose of the olgiosaccharide chain to produce A antigen.
what must be present for the A enzyme to produce the A antigen?
H antigen
What enzyme does the B gene code for?
alpha 1,3-galactosyltransferase
how does alpha 1,3-galactosyltransferase work to produce B antigen?
Uses H antigen as a substrate, and catalyses the addition of the sugar D-galactose to the final galactose of the olgiosaccharide chain to produce B antigen
What must be present in order for the B enzyme to produce B antigen?
H antigen
What is the possible genotype if you have A blood type?
A/A or A/O
What is the possible genotype if you have B blood type?
B/B, B/O
What is the possible genotype if you have AB blood type?
A/B
What is the possible genotype if you have O blood type?
O/O
Write a note on the genetic profile of the Bombay blood group
This group is quite rare. They are homozygous for the h allele, meaning they lack the H gene. They cannot form the H antigen (precursor of A and B antigens).
which blood type does Bombay O group as?
Groups as type O as it is not agglutinated by anti A or B, or anti H
are ABO antibodies naturally occurring or immune occurring?
naturally occurring but are thought to be stimulated by substances that are everywhere in nature (environmental antigens)
How soon after birth can ABO antibodies be found?
3-6 months
Are all ABO antibodies IgM?
Most are IgM, but some people have IgG at low levels
What is direct agglutination?
A test which looks for serum antibodies
at what temperatures do antibodies react at?
4-22 degrees centigrade but can also react at body temperature as they are potent
where might an absence of ABO antibodies be found?
new borns, infants, patients with hypogammaglobinaemia or patients in chemo/radium treatment. May also be in elderly patients as levels may fall with increased age.
what is a gammaglobin
an antibody
Is it mandatory to use anti AB in cell grouping?
no
Why might forward and reverse grouping not match?
If an infant <6 months old blood is tested
Why should reverse grouping not be carried out on infants <6 months?
They don’t have any anti-A or anti-B antibodies
Which groups of people have weak reactions for reverse grouping?
Elderly, immunocompromised and newborns
How does antibody specificity work?
The variable region (sequence of amino acids) corresponds to specific antigen
