Transcript ABO Discrepancies

ABO Discrepancies
Dr. MH Saiemaldahr
Blood Bank
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ABO Antibodies
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Generally IgM class antibodies
For Group A and Group B persons the predominant
antibody class is IgM
For Group O people the dominant antibody class is IgG
(with some IgM)
React best at room temperature (22-24oC) or below in
vitro.
Activates complement to completion at 37oC
Can cause acute Hemolytic Transfusion reactions
RBC Immune form: Predominantly IgG
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ABO Antibodies
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Time of appearance:
Generally present within first 4-6 months of life
Reach adult level at 5-10 years of age
Level off through adult life
Begin to decrease in later years: >65 years of age
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A and B Subgroup
They both react strongly with reagent anti-A.
80% of group A individuals phenotype as A1
20% phenotype as A2
Reagent anti-A is a mixture of two Abs ;
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anti-A which react with both A1 and A2 cells.
anti-A1 which reacts with A cells but not with A2 cells in
simple testing .
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A and B Subgroup
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Qualitative difference due to ;
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1-8 % of A2 and 22-35 % of A2B individuals produce a
readily identifiable anti-A1 in their serum.
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Quantitative difference
A2 cells carry 25 % as many A antigen sites as do A1 cells
A1 individuals make A antigen from all type II chains
( H1-4 ) .
A2 individuals produce A antigen only from H1 and H2
precursors.
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A and B Subgroup
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Differentiation between the A blood subgroups
Reagent anti-A is a mixture of two Abs
The two Abs can be functionally separated by adsorption
with A2 cells.
Anti-A1-lectin: is another source of anti-A1.
lectins are seed extracts that agglutinate human cells
with some degree of specificity.
The seeds of the plant Dolichos biflorus serve as the
source of the anti-A1 lectin this reagent agglutinate A1 or
A1B cells but does not agglutinate A2 or A2B cells.
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A and B Subgroup
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Other A subgroups: RBC of the A int, A3, Ax, Ay or A cl. are
only rarely seen in transfusion practice.
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Subgroup of B: infrequent than the weaker subgroup of
A, identified by anti-B and anti-A,B. Subgroups B3 , Bx ,
Bm and Bcl .
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ABO Discrepancies
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ABO discrepancies happen when there is no match in
results between forward and reverse grouping.
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ABO discrepancies are usually technical in nature and
can be simply resolved by correctly reporting the testing
and carefully checking reagents with meticulous reading
and recording of results.
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ABO Discrepancies
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There are some ABO discrepancies that can happen due
to technical errors and may lead to false positive or false
negative reactions.
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False positive reactions are due to;
 Un-calibrated centrifuges
 Contaminated reagents
 Dirty tubes or glassware
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ABO Discrepancies
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False negative reactions can be due to many causes
Failure to add serum or reagents
 Use of incorrect reagents or samples
 Cell suspension is too heavy or too light
 Inadequate identification of samples or test tubes
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ABO Discrepancies
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Group I discrepancies
These discrepancies are between forward and reverse
grouping due to weak reaction or missing antibodies.
These kind of discrepancies are the most common.
The reason for the missing antibody or weak reaction is
that the patient has depressed antibody production or
cannot produce the ABO antibodies.
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ABO Discrepancies
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This type of discrepancy can be seen in new born
infants, elderly patients.
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Patients with lymphoma.
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Patients using immunosuppressive drugs.
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Patients with immunodeficiency disease, BM transplant.
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ABO Discrepancies
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Resolving discrepancies
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Eliminate all technical errors
Enhancing the reaction in reverse grouping
Incubate the patient’s serum with reagent cells at room
temp. for 15 mins.
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ABO Discrepancies
Group II discrepancies
These discrepancies are between forward and reverse
grouping due to weak reaction or missing antigens.
This group is the least one. Can be caused by some
subgroups of A or subgroups of B or both.
Also it can be present in patients with leukaemia and
hodgkin’s disease.
To resolve the problem wash the patient’s cells with saline.
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ABO Discrepancies
Group III discrepancies
These discrepancies are between forward and reverse
grouping due to protein or plasma abnormalities.
These can be caused by elevated levels of globulin from
certain diseases such as multiple myloma, hodgekin’s
lymphoma. Some are caused by (Rouleaux formation).
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ABO Discrepancies
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Rouleaux or red cells result from a stacking of
erythrocytes that adhere in a coin-link fashion giving the
appearance of agglutination.
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To resolve this kind of problem, washing the patient’s
red cells with saline or adding a drop or two of saline to
the tube in case of rouleaux formation.
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If the agglutination is true red cell clumping will remain.
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Cord blood must be washed 6-8 times in forward
grouping ONLY.
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ABO Discrepancies
Group IV discrepancies
 These kind of discrepancies are between forward and
reverse groping due to miscellaneous problems.
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Polyagglutination can occur due to exposure of hidden
erythrocyte Ag. (T antigen) in patients with bacterial or
viral infection.
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Bacterial contamination in vitro or vivo produces an
enzyme that alters and exposes the hidden Ag. on red cell
leading to T activation.
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ABO Discrepancies
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Some examples of discrepancies
 Example
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Forward grouping: anti-A =O, anti-B =O, anti-AB= O
Reverse grouping: A1 cells= O, B cells =O
Blood group:
O
Possible discrepancy:
Missing Ab. Or group I discrepancy
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ABO Discrepancies
 Example
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Forward grouping: anti-A = 4+,anti-B =O, anti-AB =4+
Reverse grouping: A1 cells =1+, B cells =4+
Blood group:
A
Possible discrepancy:
Missing Ag. Or group II discrepancy
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ABO Discrepancies
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Example 3
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grouping: anti-A 4+,anti-B 2+,anti-AB 4+
 Reverse grouping: A1 cells 4+, B cells 4+
 Blood group : A
 Possible discrepancy
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Rouleaux formation
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