Abo blood group _ Amanda Flashcards
Landsteiner’s Law
“If an antigen is present on the RBC of an individual, the corresponding antibody must be absent in the plasma of that individual and vice-versa.”
Landsteiner’s Law example
Individual with A antigen on their RBC, hence blood group A, will have anti-B in their plasma
Where is the ABO locus located?
ABO locus located on chromosome 9
What deletion causes a frame shift resulting in the group O phenotype?
Deletion at residue 261 causes a frame shift
How many allelic forms does the ABO locus have?
3: A, B, and O
What do the A and B alleles each encode?
Glycosyltransferase that catalyses the final step in the synthesis of the A and B antigen, respectively
What is the expression of A and B dependent upon?
A precursor H substance
What do group O individuals lack?
Active enzyme
Where is the H gene (FUT) located?
Chromosome 19
What does H gene code for?
- inherited independently
- codes for an enzyme that converts carbohydrate precursors into H substance
What do the A and B genes code for?
- specific enzymes that convert H substance into A and B antigens
How is the blood group O achieved in an individual?
O gene produces an inactive transferase so H substance persists unchanged
Type-1 chain basic precursor for ABH antigens
Beta (1-3) linkage
Type- 2 chain basic precursor for ABH antigens
Beta (1-4) linkage
What enzyme is involved in the formation of H antigen?
L Fucosyl Transferase enzyme (product of H gene)
What enzyme is involved in the formation of the A antigen?
N-acetylgalactosaminyl transferase (product of A gene)
What enzyme is involved in the formation of the B antigen?
D-galactosyl transferase (product of B gene)
Why do Group O invidiuals have more H antigen than the other groups?
O gene is a silent allele.
Does not alter the structure of the H substance, so more H antigen sites
What is the Bombay phenotype ?
Individuals whose RBCs lack the H antigen.
Described as Ohh
Why does the Bombay phenotype RBCs also lack A and B antigens?
A and B antigens cannot be formed without the H antigen precursor
What is the result of the Bombay phenotype?
O phenotype- since lack of A and B antigens
Produce anti-H
Leucocytes
Lymphocytes acquire A, B and H antigens from the plasma of secretors
Granulocytes and monocytes
Don’t express ABH antigens
Platelets
Express ABH antigens on glycolipipds and the platelet glycoproteins
Where is Blood group O frequency highest and lowest?
Highest- Nigeria
Lowest- India
Where is Blood group A frequency highest and lowest?
Highest- Turkey, Denmark and France
Lowest- Nigeria
Where is Blood group B frequency highest and lowest?
Highest- Pakistan
Lowest- Australia, Denmark, France and USA
Where is Blood group AB frequency highest and lowest?
Highest- India
Lowest- Iran
Blood group antibodies can be classified into:
Non-immune (Naturally occurring)
Immune antibodies
- cold and warm
What are naturally occurring antibodies usually?
IgM (cold)
What are non-immune antibodies
-ABO
-Predominantly IgM although some IgG
- produced early in neonatal period following colonisation of gastrointestinal system with bacteria
What are immune antibodies?
- develop in response to the incompatible red cells- by transfusion or transplacental passage during pregnancy
- antibodies commonly IgG, although some IgM
What immune antibodies are the only one capable of transplacental passage from mother to foetus?
IgG
What is an important immune antibody?
Rhesus antibodies, especially anti-D
What serological methods are used in ABO blood grouping?
- test patient red cells with known antibodies for presence of A or B antigens (cell or forward group)
- test patient’s serum for presence of Anti A and/or Anti-B antibodies by testing against cells of known red cell phenotype ( serum or reverse group)
Molecular typing techniques?
Identification of gene sequences on chromosome 9 that confer ABO phenotype
- not widely used currently due to the multiple genetic variations that phenotypically give rise to the A, B, AB and O groups
ABO incompatibility
- the rapid intravascular haemolysis which occurs in ABO incompatible transfusions can precipitate severe disseminated coagulation (DIC), prolonged hypotension, acute uraemia, and event death
Why are ABO antibodies of major clinical significance?
- naturally occurring and found universally
- highly reactive, complement activating
- transfusing a patient with the incorrect ABO blood group may have fatal consequences
- incompatible donor red cells may be rapidly destroyed by anti-A or anti-B antibody in the recipients plasma
What shoul blood grouping and identifying compatible blood components prevent?
Adverse transfusion reactions caused by ABO antibodies, however, clerical error can result in the “wrong blood” being transfused into a patient, an error which can result in patient death
Serological compatibility testing
The patients plasma, containing antibodies, is tested against the red cells of the donor to determine if there is going to be a reaction
Electron issue compatibility testing
- for patients who don’t have any history of having red cells antibodies and don’t have any unexpected antibodies in their current plasma sample
- patients and donors are matched electronically for ABO and RhD with no physical cross match performed
Antibody screening - blood group of patient is determined and screened for atypical antibodies
If antibody screen positive- crossmatched
If antibody screen negative- electronic issue
If blood is required before cross matching can take place, group O is given
