Transcript ABO & Rh Discrepancies

ABO & Rh Discrepancies
Definition

When the results of the forward grouping (patient
cells) do not correspond to the results of the reverse
grouping (patient serum) or abnormal reactivity is
present (i.e. Mixed Field)

i.e. the forward does NOT match the reverse
Patient
Anti-A
Anti-B
A-Cells
B-Cells
A
4+
1+
0
4+
B
0
4+
1+
0
C
4+
4+
1+
0
D
0
3+
0
0
Patient A: Additional reaction with anti-B and patients cells.
Patient B: Weak reaction with patients serum and A-cells.
Patient C: Additional reaction with patients serum and
A-cells.
Patient D: Missing reactions with patients serum A-cells
ABO Discrepancies must be resolved

In RECIPIENTS the discrepancies must be resolved
before any blood component is transfused.
–

If not resolved before blood is needed, transfuse Group O
(O NEGATIVE if there is a discrepancy in the Rh type
also).
In DONORS the discrepancies must be resolved before
any blood is labeled with a blood type.
Categories of ABO Discrepancies
A.
B.
C.
D.
Cell Typing – Additional Reactions
Cell Typing – Missing Reactions
Serum Typing- Additional Reactions
Serum Typing- Missing Reactions
A- Cell Typing: Additional Reactions
1- Polyagglutinable Red Cells
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ANTI-A
ANTI-B
A CELL
B CELL
4+
4+
0
4+
The removal of red cell N-Acetyl neuraminic acid by
bacterial enzymes expose the T-Ag on the cell membrane.
Antibodies to T-antigens are naturally present in most
human sera.
This Ab can also be found as a contaminant in some ABO
typing reagents.
This cause unexpected agglutination of T Ags on red cells.
2- Acquired Antigens
•
•
•
•
ANTI-A
ANTI-B
A CELL
B CELL
4+
2+
0
4+
Microbial deacetylating enzymes such as E. coli cleave
off the N-Acetyl of the Group A N-acetyl-galactosamine
The remaining galactosamine becomes similar to the
Group B galactose
Anti-B react with this B-like Ag causing agglutination
A-like Ag can also be acquired
Group A
individual
N-acetyl galactosamine
Bacterial enzyme
removes acetyl group
Acquired
B
Phenotype
Galactosamine
now resembles
D-galactose (found
in Group B)
3- Non-specific Agglutination
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

Wharton’s Jelly – gelatinous substance derived
from connective tissue that is found in cord blood
and may cause false agglutination
Wharton’s Jelly Coats newborn cord cells and the
child's type may appear AB.
We do not do a reverse on newborn blood since
they have not made any anti-A or anti-B yet.


If the baby types as an AB recheck by washing
cells several times and re-testing since you need
to make sure you have removed the Wharton's
Jelly and the baby is truly an AB.
Better ALWAYS wash cord blood at least 4 to 5
before determining the type of the baby, or
request new sample from heel
4- Sensitized Red Blood Cells



Albumin in the ABO typing reagent can reduce
the zeta potential
Effectively decreases the distance between red
cells.
If the red cells are coated with antibody, false
positive agglutination can occur
B- Cell Typing Missing Reactions
1- Subgroups




ANTI-A
ANTI-B
A CELL
B CELL
0
0
0
4+
Weak variants of both A & B
Carry poorly expressed Ags
May not produce expected reactions with anti-A &
anti-B
They are categorized according to the strength and
pattern of reaction with anti-A, anti-H & anti-A,B
2- Altered Antigen Expression
ANTI-A
ANTI-B
A CELL
B CELL
0
0
0
4+
• Weak Ags may be found on RBCs of some
people with diseases (Leukemia)
3- Chimera

Chimera: Two cell populations
–
Natural Chimera:
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
–
In utero exchange of erythropoetic tissue between
non-identical twins
Strength of reaction with ABO typing depends on
the percentage of A or B cells in blood
Temporary Chimera:
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following blood transfusion of ABO compatible,
but not identical blood ( A received O cells)
4- Excessive amounts of group specific substances


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Patients with certain types of cancer
Large amounts of soluble A or B Ags
Inhibit anti-A or anti-B typing reagent
Can be resolved by washing RBCs prior to ABO
typing
C- Serum Typing Additional Reactions
1- Alloantibodies




Abs other than anti-A or anti-B
Can agglutinate A or B cells if express specific Ag
Abs commonly cause this discrepancy anti-M, -N,
-S, -Lea, Leb, -P1, A1
Can be identified by testing serum with a panel of
O cells that have been phenotyped for these Ags
2- Autoantibodies



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IgM autoantibodies can cause false-positive results
in cell & serum grouping
Problem can be solved by washing cells with warm
saline prior to testing
In serum typing, autoabsorption can be performed
Or serum typing at 37oC
3- Rouleaux formation
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ANTI-A
ANTI-B
A CELL
B CELL
4+
0
2+
4+
Rouleaux may also give false positive cell typing if strong
enough
Looks like agglutination macroscopically
This phenomenon is due to alteration in serum protein
concentration caused by:
– elevated levels of gammaglobulins
– elevated levels of fibrinogen
– Also seen with plasma expanders (dextran)
Cell grouping- can be avoided by washing RBCs
Serum grouping- addition of saline
D- Serum Typing Missing Reactions
1- Newborns


Infants develop ABO Abs by 3-6 months of age
Serum typing before this time:
–
–
Weak reaction
Negative reaction
2- Patients with Hypogamma-globulinemia


Have low levels of immunoglobulins
Anti-A & anti-B may not be detected
3- Chimera


Twins that have chimeric blood group can lack A
& B Abs
Chimera with 98% O cells & 2% B cells
–
–
Group as O
Serum contain only anti-A
4- Reagent Problems

Deterioration of Ags on A or B cells used for
serum typing
–
–
Weak
Negative reaction
Rh Discrepancies

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Rh –ve persons mistyped, & transfused with Rh
+ve blood have 70% chance of becoming
immunized
False +ve reactions can be identified by testing an
Rh control with the patient’s red cells each time
an Rh typing is performed
The test is not valid if the control causes
agglutination
Causes of false positive reactions
1.
2.
3.
Positive direct antiglobulin test
Polagglutinable red cells
Cold agglutinins or Rouleaux formation
1- Positive direct antiglobulin test
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
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The presence of Ab on patient’s red cells can cause
a false +ve reaction with slide and tube anti-D
High protein medium reduces zeta potential
allowing red cells to move closer
The cell bound Ab can cross link cells and cause
agglutination
2- Polagglutinable red cells
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
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Rh –ve red cells that are polyagglutinable due to T
or Tn activation
Agglutination occurs if anti-T or anti-Tn present in
the anti-D reagent
Most anti-D reagents do not contain these
antibodies
3- Cold agglutinins or Rouleaux formation
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Rh typing is performed using serum suspended
red cells
If individual’s serum contains cold agglutinin or
abnormal protein, false positive reactions can
occur