LA2 ABO Blood Group System Flashcards
Acute hemolytic transfusion reaction
Complication of transfusion associated with intravascular hemolysis, characterized by rapid onset
with symptoms of fever, chills, hemoglobinemia, and hypotension; major complications include irreversible shock, renal failure, and disseminated intravascular coagulation.
Universal donor
Universal donor for RBC transfusions is group O; universal donor for plasma transfusions is group AB.
Universal recipient
Universal recipient for RBC transfusions is group AB; universal recipient for plasma transfusions is group O.
Forward grouping
Use commercially prepared anti-A and anti-B to test patient cells for A and B antigens.
Reverse grouping
Use commercial A-cells and B-cells to test patient’s plasma for anti-A and anti-B.
Landsteiner’s Law
Normal, healthy individuals will have ABO antibodies to the ABO antigens which are lacking on their red blood cells.
Formation of H antigens
End-product of an enzymatic reaction: transferase enzymes promote attachment of immunodominant sugar (fucose) to precursor substance (4-sugar chain) on RBCs membrane.
Immunodominant sugar fo A antigen
N-acetylgalactoseamine (“GalNac”)
Immunodominant sugar for B antigen
D-galactose
Immunodominant sugar for H antigen
Fucose
When do ABO system antibodies start to present in the blood?
After ~4 months.
At what age do ABO system antibodies reach their highest titre?
5-10 years
What happens with ABO system antibodies as the people grow older?
ABO antibodies titre gradually declines with age.
Clinical significance of ABO system antibodies
1) Very good at activating complement cascade and causing intravascular hemolysis -> AHTR (acute hemolytic transfusion reaction)
2) Can agglutinate RBC’s directly
3) Best at RT and don’t need incubation time, but also react at 37C (body temp)
Frequencies of ABO blood types
Most common - O (~40%); then A, B; least common - AB (4-5%).
Ulex europaeus
Plant lectin with specificity for the H antigen (reacts with H antigen on RBCs surface).
How is reverse grouping related to forward grouping?
Reverse grouping is a control for forward grouping.
Why reverse grouping is not done on infants younger than 4 months old?
Because they don’t have any ABO antibodies yet.
Formation of A and B antigens
Transferase enzymes attach A or B immunodominant sugar to the H antigen on RBCs membrane.
Anti-H
Ulex europaeus lectin. Usually used to test to see amount of H antigen on the patient’s RBCs.
What immunoglobulin class are anti-A and anti-B?
IgM, with the exception in group O person - IgG
How does the H antigen concentration vary in ABO phenotypes?
Group O - no sugars added, therefore all antigens remain H antigens. Group AB - most H antigens are converted to A or B antigens, therefore fewest number of H antigens left.
Formation of ABO system antibodies
Produced as a result of exposure to environmental factors which have similar biochemical structures to the A and B antigens.
Non-red cell stimulated antibodies
Antibodies produced without exposure to other person’s RBCs.
Anti-A,B
Additional antibody made by group O individuals only. Reacts with A antigens and/or B-antigens.
When performing ABO-typing, which stage of agglutination is enhanced by centrifuging the tests?
Lattice formation
What is the minimum reaction strength which must be obtained in the forward ABO grouping to call it positive without further testing?
3+
What is the minimum reaction strength which must be obtained in the reverse ABO grouping to call it positive without further testing?
2+
What should be done if the result obtained in reverse ABO grouping doesn’t “match” forward ABO grouping for that patient?
Repeat both tests.
Lectin
A protein derived from a plant which reacts with red cell antigens.
Possible genotype for A group
AA or AO
Possible genotype for B group
BB or BO
What is a Bombay phenotype?
Phenotype corresponding to hh genotype (absence of H gene).
What would be result of Ulex europaeus test with a Bombay phenotype blood?
Negative
What would a Bombay phenotype look like in ABO forward testing?
Like group O. In Bombay phenotype, RBCs lack H antigens, so terminal sugars cannot be added to get A o B antigens.
Which ABO antibodies does a Bombay phenotype person have?
Anti-A, anti-B, anti-A,B, and anti-H
Who can become a donor for a Bombay phenotype person?
Only another Oh person:
- check siblings, rare donor banks
or - patient can make autologous donations for future use
What are the typical reactions for a Bombay phenotype in ABO typing?
–A : 0 ; –B : 0 ; –A,B : 0 ; AC : 4+ ; BC : 4+ ; OC : 4+
What would the phenotype be for AAhh genotype?
Oh - Bombay phenotype.
